Europaisches Patentamt 0196 347 J European Patent Office (11) Publication number: B1 Office europeen des brevets

EUROPEAN PATENT SPECIFICATION

L 11/16 (§) Date of publication of patent specification: 16.08.89 Int.•Cl.4: H 04 B 9/00, H 04

(3) Application number: 85103928.9 (2) Date of filing: 02.04.85

Infrared communication system.

Date of publication of application: Proprietor: International Business Machines 08.10.86 Bulletin 86/41 Corporation Old Orchard Road Armonk,N.Y. 10504 (US) Publication of the grant of the patent: 16.08.89 Bulletin 89/33 Inventor: Gantenbein, Dieter SpyristrasselO Designated Contracting States: CH-8044 Zurich (CH) DEFRGB Inventor: Gfeller, Fritz Rudolf, Dr. 1509 Eagle Bay Drive OssiningN.Y. 10562 (US) References cited: Inventor: Mumprecht, Eduard Peter, Dr. EP-A-0054 582 Schwabach 65 DE-A-2431937 CH-8706 Feldmeilen (CH) PROCEEDINGS OF THE IEEE, vol. 67, no. 1 1, November 1979, pages 1474-1486, New York, (74) Representative: Mohlen, Wolfgang C, Dipl.-lng. US; F.R. GFELLER et al.: " in-house IBM Corporation Saumerstrasse 4 via diffuse infrared CH-8803 Riischlikon (CH) radiation" IBM TECHNICAL DISCLOSURE BULLETIN, vol. (58) References cited: New 24, no. 8, February 1985, pages 4043-4046, JOURNAL OF LIGHTWAVE TECHNOLOGY, York, US; F. GFELLER: "Infrared 1, February 1985, 93-100, data vol.LT.3, no. pages CO microbroadcasting network for in-house IEEE, New York, US; S. MOUSTAKAS et al.: communication" "Passive optical star bus with collision O) detection for CSMA/CD-based local-area networks" Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been convention). Ill paid. (Art. 99(1 ) European patent Courier Press, Leamington Spa, England. EP 0196 347 B1

Description

Field of the invention The present invention is related to communication systems, and more particularly to a communication 5 system interconnecting data transmitting and receiving units by infrared signals, and to a method of transmitting data in a system comprising a plurality of units including stations and associated devices.

Background of the invention The use of infrared signals for exchanging information between devices has received increased 10 interest during recent years. The advantage of such systems is the elimination of special signal transmitting media such as wires. With respect to radio frequency (RF) transmission, infrared (IR) transmission has the advantages that no communication regulations apply and no PTT or FCC license is required, no disturbance by EMI and no interference from other RF channels can occur, and the radiation is confined to a room so that better data security is available than with RF systems. 15 Several IR transmission systems were described in the literature and disclosed in patents. An article by F. Gfeller and U. Bapst entitled "Wireless In-House Data Communication via Diffuse Infrared Radiation", published in Proceedings of the IEEE, Vol. 67, No. 11, Nov. 1979, pp. 1474...1486 describes a communication network in which data are transferred between a plurality of terminals and a host computer. Each room in which terminals are located comprises a satellite station which receives IR 20 signals from and distributes IR signals to the terminals. All satellites are connected to the host by an electrical wire network. No direct communication between terminals is provided. In U.S. Patent 4,402,090 (& EP— A— 54582) entitled "Communication System in which Data are Transferred Between Terminal Stations and Satellite Stations by Infrared Signals", as well as in an article by F. Gfeller "Infranet: Infrared Microbroadcasting Network for In-House Data Communication", published 25 in Proceedings, 7th European Conference on Optical Communications, Sept. 1981, pp. P27-1...P27-4, a similar system is described which however provides a plurality of satellite stations for a large room to enable coverage of the larger area which is not possible with a single satellite. Though this prior art solves the problem of possible multiple reception of the same message via the IR channel, it does not provide for direct communication between the terminal stations. 30 With the rapidly increasing number of intelligent workstations and personal computers in all areas of business, administration, etc. there is also an increasing need for connecting I/O devices such as keyboards, displays, printers to them, and for interconnecting such workstations and small computers to each other. The use of electrical wire networks becomes a problem in particular with high density of stations and in the many cases where the location of stations or the configuration of subsystems must be 35 changed frequently. It is therefore desirable to use IR signal transmission for interconnecting such devices and workstations to eliminate the requirement of electrical cable networks. A problem, however, is the possible mutual interference of infrared signals if several connections are to be maintained simultaneously which is necessary e.g. in a large office environment. Frequency is not possible because there is not enough so that all devices must use the same 40 baseband channel.

Objects of the invention It is an object of the invention to provide a communication system exchanging information between several data handling units, which is based on infrared signal transmission and allows efficient data traffic 45 despite a great number of participating stations. It is another object to devise an IR local communication network that allows an orderly access to the infrared transmission medium even if the transmitted IR signals that are received by any unit from different devices or stations are of considerably different strength. Another object of this invention is an IR communication system that allows selective paths or so configurations to be established by device selection to avoid the distribution of IR signals representing data packets to units where they are not required to go thus reducing the chances of interference between different communication sessions. It is a further object to provide an IR communication network design that allows to interconnect a large number of workstations and I/O devices of different capabilities, distributed over an extended area, with a S5 minimum in mutual disturbance. It is another object to provide a communication system which can exchange data between several data handling units, providing above mentioned features and which uses for the transmission of data signals either the infrared medium exclusively or mixed media including cables, so that some units may be interconnected by infrared means and others by wires, depending on the transmission distance and other eo- considerations. Disclosure of the invention According to the invention, transceivers of data transmitting and receiving units are assigned to different categories having a hierarchical scale of transmission power and receiving sensitivity, so that 65 some data transmissions are only effective in close neighbourhood thus allowing simultaneous EP 0196 347 B1

transmission in different local regions, whereas also data communications from one end of the system to the other are possible. To allow orderly access even if data of an ongoing transmission are not correctly received, each unit that detected a preamble carrier signal preceding each packet transmission observes a time-out and simultaneously tries to decode received data signals and their end delimiter so as to have at 5 least one of two possible bases for establishing a reference point for a subsequent attempt to access the transmission medium, without interfering with an ongoing transmission. The provision of selecting or enabling bits in each transmission frame allows to selectively activate (or inhibit) units that may be receiving the frame but should not use or forward it. The IR transmission network architecture introduced by the invention supports slow, battery-powered and 10 devices as well as fast, balance-mode communication between workstations. All kinds of stations devices can use the infrared channel in a common way. An embodiment of the invention is described in the following detailed description and will more clearly and of the present in connection with the accompanying drawings the different features advantages invention. 15 Brief description of the drawings Fig. 1A...1D illustrate the different possible configurations of an IR communication network utilizing the invention; Fig. 2 schematically shows a workstation and its transceivers that are used in present embodiment of 20 the invention; Fig. 3 shows the frame format used for packet transmission in the IR network; Fig. 4 illustrates the transmission model with different ranges that are distinguished in a system using the invention; Fig. 5 is the block diagram of an infrared transceiver used in the disclosed embodiment; 25 Fig. 6 is a diagram of the interface signals that are transferred to and from the IR transceiver of Fig. 5; Fig. 7 shows the packet format used for data transmission, including the mode field which accomodates bits for selecting or enabling specific units in the system; Fig. 8 is a time diagram illustrating the access protocol introduced by the invention; Fig. 9 is a diagram of the different states and transitions that are possible in a transceiver when the 30 invention is used; Fig. 10 is a flowchart illustrating the access protocol procedure; and Fig. 11 is a block diagram of logic circuitry embodying the access protocol of the invention.

Detailed description 35 A. Principles 1. System overview There are several possibilities for the integration of workstations into a single IR network, as shown in the different parts of Fig. 1. Fig. 1A shows two independent workstations each consisting of a system unit 11 and one or several 40 peripheral devices 13, 15. Keyboards 13 (KB) and printers 15 (PR) are connected to the respective system units 11 (SYS) cordless via infrared (IR) signals. Workstations can have several IR-attached peripheral devices at a time, e.g. keyboards, mice (pointing devices), printers, and displays. The workstations operate independently of each other. Nevertheless, IR interferences can occur if they are too close to each other. Such an interference between a keyboard and a system unit is drawn in Fig. 1A as a dotted line. Key 45 requirements for IR-attached keyboards are low cost and low power consumption (because they are batery-powered). In order to reduce interferences between workstations, both, local devices and system unit have low-range transceivers. Workstations that want to communicate with each other need a transceiver with more optical power as shown in Fig. 1B. Such a transceiver can be installed as an option in each system unit 11. Alternatively, a so single high power transmitter is installed but powered with two different power levels, according to communication requirements. Workstations that are too far away from each other cannot communicate directly. Fig. 1C shows a possible solution for this problem, in which an asynchronous repeater 17 (REP) is provided which forwards traffic between stations. Several repeaters could be used for covering larger areas. forward traffic 55 Fig. 1D shows a system with a back-to-back pair of special repeaters 19, 21 which through a wall. A similar setup can be used for a gateway 23 to another network, e.g. to a ring or a bus , or any other cable-bound subnetwork comprising one or several workstations. Of course, any one of the IR connections shown in Figs. 1A...1D could be replaced by a wire connection if that is desirable and advantageous. 13 is shown in 2. 60 A possible assembly of system unit 1 1 with a display unit 12 and one keyboard Fig. The system unit comprises two microprocessors 25, 27 (MP) interconnected by a system bus 29. A transceiver 31 for exchanging IR signals with other workstations or with a repeater is connected to microprocessor 25, and a second transceiver 33 for exchanging IR signals with local devices is connected to microprocessor 27. Both IR transceivers 31 and 33 within the system unit are independently addressable, 65 from the microprocessors as well as from the IR network. EP 0196 347 B1

In a mixed media system, transceivers 33 and 35 could be replaced by cable transceivers for interconnecting the device to its system unit by cable, or transceiver 31 could be replaced by a cable transceiver to allow interconnection of several system units by a cable bus. Keyboard 13 (as well as each other local peripheral device) comprises a transceiver 35 for exchanging 5 IR signals with the system unit transceiver 33.

2. Transmission format and speed of infrared transmission This section describes the transmission format and discusses the possible speed of the IR transmission. 10 2.1 Transmission format The structure of the basic frame format is shown in Fig. 3. Manchester coding is used for data transmission over the IR channel. A preamble consisting of a sequence of alternating ones and zeros (at least five ones) serves to settle the analog front-end of the receiver to its equilibrium state and also 15 indicates the presence of a carrier. More generally, the preamble is a sequence of rectangular pulses of 50% duty cycle emitted at Manchester bit rate. Carrier in this specification means the presence of a transmission on the ether, i.e. in the infrared transmission "channel". The synchronization pulse start delimiter consists of three consecutive zeros followed by three consecutive ones and is interpreted as a code violation and is therefore transparent. The subsequent data bits are encoded in Manchester code (i.e. 20 each data bit being represented by a 0/1 or 1/0 pair of half-bits) which facilitates clock extraction and allows ac-coupling. (Another possible candidate is pulse position coding). The data packet format is described in detail in section 6. The end of the transmission is signalled by the end delimiter code violation which is different from the start delimiter code violation. It allows to determine the end of a packet, and is a synchronization event to start counting access slots. 25 2.2 Speed Investigations have shown that the diffuse IR channel has a bandwidth of approximately 10 MHz (restriction due to multiple optical paths of different lengths). In practice, however, the transmission speed is limited to 1 MBit/s due to the limited modulation capability of high output power, low-cost light emitting 30 diodes (LEDs). The wide-spread use of such LEDs (TV remote control and the like) has rendered a very low production cost. Another restriction is given when microprocessors with slow serial input and output ports are used. For the present embodiment, a data rate of 375 kBit/s was selected. However, the possible data rate of 1 MBit/s could be utilized if buffers are provided at the I/O ports, or if microprocessors with faster I/O ports are provided. 35 The packets are emitted in short bursts of up to 128 data bytes resulting in transmission durations of 2 to 4 milliseconds maximum. This allows to drive the LEDs with current pulses up to 2A. The thermal time constant of an LED is approximately 2 to 3 ms, thus preventing overheating of the junction. For repetitive packet transmission, the packets are transmitted with a duty cycle of 10% to allow cooling of the LED. The interval between packets of maximum length is therefore 20 ms to 40 ms. During these intervals other 40 stations may contend for access to the IR channel. The sustained data rate between stations is therefore 37.5 kBit/s (minus protocol overhead) for the 375 kBit/s speed and up to 100 kBit/s for the maximum speed of 1 MBit/s.

45 3. Specifications for different ranges The different configurations of the infrared transmission network given before (Fig. 1) specify three physical transmission ranges:

3.1 "LAN on a Table" 50 This range is allocated to the peripheral input/output devices which normally have to be within close range of the system unit of the workstation, such as keyboards, joy-sticks, touch panels. The display unit can also be allocated to this class. The indirect (diffuse) range is approximately 2... 4 m, with direct line-of-sight transmission up to 8 m. Optical transducer requirements per transceiver: 55 * 2 LEDs * 2 Photodiodes.

3.2 "Intra office LAN" This range (indirect 10...12 m) is allocated to peripheral devices which need not (or should not) be eo close to the system unit of the workstation. Printers, plotters, and other input or output devices are examples. This range should cover medium sized office rooms without repeaters. The transceivers could be plugged in as separate units at the back of the device (as shown for the system unit in Fig. 2). Optical transducer requirements per transceiver: * 12 LEDs 65 * 4 Photodiodes. EP 0196 347 B1

3.3 "Intra office LAN with repeaters" A typical example would be a classroom or auditorium environment. A repeater may have a transmission (and receiving) radius of more than 1 5 m. The repeater has a separate power supply, standing in on a desk or mounted on a wall or ceiling. Alternatively, the repeater function can be incorporated a be used 5 system unit to save the extra cost for separate housing and power supply. Several repeaters may office and low to cover open space large office areas measuring 30x30 m. Alternatively, cluttered spaces "hidden" stations. partition walls may require multipath transmission via several repeaters to access Optical transducer requirements per transceiver: * Nx24 LEDs (arranged in a circular array) w * 12 Photodiodes. The factor N refers to the fact that the packet duty cycle for repeaters is 50% since in the interest of an N=2...3. optimally used channel capacity they have to retransmit received packets immediately. In practice The numbers indicated for LEDs and photodiodes are approximate and refer to a transmission speed of 375 kBit/s under daylight (no direct sun light on photodiodes) or fluorescent lighting conditions. Each LED 15 will emit approximately 250 mWatt peak power and the sensitive area of each photodiode is approximately 10mm2. The transducers of the "Intra Office LAN" type, i.e. workstation transceivers, must be flexibly mounted to allow their beams pointing towards the interior of the office. i.e. The ranges referred to correspond to the "D-boundaries" (see following section), they are physical domains. 20 4. Transmission model The IR channel is more complex than a bus. The characteristics of transceivers and medium cannot is guarantee that each pair of devices can communicate. Nevertheless, a global addressing scheme required. sender 25 Fig. 4 schematically shows the different levels of direct reachability that can occur between a and a potential corresponding receiver device. (Generally, the scale, i.e. the radius of the ranges, depends on both, the sender power and the receiver sensitivity). * A receiver inside the D-boundary (data boundary) can fully recognize/decode the data signal and thus can receive data frames correctly. The end of transmission (end delimiter) is safely detectable 30 within this range. * A receiver between the D-boundary and C-boundary (carrier boundary) can just sense the carrier (i.e. the preamble), but not correctly decode data. In particular, the end of transmission (end delimiter) cannot be detected. * A receiver between the C-boundary and N-boundary (noise level boundary) cannot sense the interference 35 preamble correctly. However, the signal is still above the noise level and may cause with other ongoing transmission. * The sender can not interfere with stations outside the N-boundary because in this range its signal is at or below noise level. Devices that want to talk to each other have to be within the D-boundaries of each other. Devices 40 outside their respective D-boundaries cannot communicate, but may still cause mutual interference as long as they are within their respective N-boundaries. Two senders transmitting at the same time can cause a collision. On a cable-bound medium this would inevitably result in both packets being destroyed. On the IR medium this is not necessarily the case. The above stronger signal will override the weaker signal provided that the stronger signal is at least 20 dB(el) the weaker one. The receiver and decoding circuitry will respond correctly to the stronger synchronization 4S actual pattern and lock to the forthcoming data stream. Depending on the relative location of the two transmitters and their two respective addressed receivers three situations may occur: Both packets are saved, one packet only is saved, or both packets are destroyed. No collision detection is provided in this system. The loss of packets will be detected by error control procedures in a higher level protocol. transmission so The transceivers of local devices have to be specified with the shortest possible range. This avoids excessive interference at other workstations and preserves their share of the IR bandwidth. If communication partners are not powerful enough to be in their respective D-boundaries, repeaters have to be installed.

55 B. Details of circuitry; packet format; and protocol 5. Transceiver circuitry 5.1 General/Basic circuitry A basic infrared transceiver circuit with receiver stage 41 , comparator 43, Manchester decoder/encoder (MDE) 45, carrier detector 47 comprising carrier sense filter 49 and threshold comparator 51, carrier sense in 5. Photodiodes 57 are 60 latch (CS latch) 53, and transmitter stage 55 is shown as block diagram Fig. provided at the input of receiver stage 41, and light emitting diodes (LEDs) 59 are provided at the output of transmitter stage 55. For all types of transceiver ranges, the circuits are identical apart from modular expansions for additional optical transducers (additional receiver and/or transmitter stages). Additional photodiodes can be connected to the receiver stage via isolating front-end circuits. Similarly, driver circuits 65 for additional LEDs can be provided at the transmitter stage. EP 0 196 347 B1

On the right side of Fig. 5, there are shown the interface lines by which the transceiver is connected to the system unit (or I/O device, respectively). The same transceiver circuit arrangement could be used for units in a cable-bound subnetwork that is connected to an IR transmission network (as was mentioned in section 1), except that IR receiver stage 41 5 with photodiodes 57 and transmitter stage 55 with LEDs 59 would be replaced by a cable receiver and a cable driver, respectively.

5.2 Circuit details for receiving and transmitting For large area photodiodes and strong input signal levels (close proximity of transmitter or strong 10 near-field echo) the front-end circuitry in receiver stage 41 may become saturated and therefore inoperational. To counteract this phenomenon a gated gain control responding to the first input pulse without delay can be provided in the receiver stage. In order to isolate the dc photo-current generated by ambient light and to reject lower frequency ac fluctuations (light intensity fluctuations of fluorescent and incandescent lamps due to the mains frequency is and higher harmonics) a first order high pass filter is provided in receiver stage 41. For Manchester encoding the pole of this filter is located at approximately 12 kHz for the 375 kbit/s speed or 30 kHzforthe 1 Mbit/s speed which provides incomplete but acceptable filtering of the "old" 50 Hz fluorescent tubes. In addition, this filter also causes a relatively long recovery time after receiving a packet. The recovery time is especially long for strong near-field echoes. During the recovery time the receiver is 20 not able to receive a weak signal. This requires the definition of a guard time in the access protocol. This guard time Tg (more details will be given in section 7 and in connection with Fig. 8) is approximately 300 microseconds. Improved filtering for the "new" type of rf fluorescent lamps, which emit weak IR radiation at 30...50 kHz and their harmonic overtones, can be achieved by differentiating the received signal pulses, or by 25 delaying the received signal by T/2 (where T is the bit duration) and comparing it with the undelayed signal. In conjunction qith the latter two filtering methods, the guard time Tg interval can be reduced to approximately 30 us by using an automatic gain control circuit. Comparator 43 compares the output signal of receiver stage 41 to the dc-restored base level and furnishes a TTL logic signal to Manchester decoder/encoder (MDE) 45. 30 MDE 45 receives a locally generated 12 MHz clock signal on line 61 from the system unit. It furnishes a bit stream representing the received data (SDO) on line 63 and a respective receive clock (DCLK) on line 65. If no data can be recognized, a signal "Non-Valid Manchester data received" (-NVM) is activated on line 67. When an end delimiter code violation is detected, a respective indication signal is issued on line 69. The decoding portion of MDE 45 is only enabled when a signal "carrier sensed" (CS) on line 71 is active. 35 For its encoding function, MDE 45 receives an enabling signal "clear to send" (-CTS) on line 73, and the bit stream of data to be transmitted (SD) on line 75 from the system unit. On line 77, it furnishes a transmit clock (ECLK) for controlling the rate of data transfer from the system unit to the MDE. On line 79, it furnishes the Manchester encoded data (-BZO) to transmitter stage 55. MDE 45 issues a pulse on line 69 not only when it received an end delimiter code violation from 40 receiver 41, but also when it furnishes an end delimiter code violation on line 79 to transmitter stage 55 (to ensure proper access timing in any case, as will be explained later). If a single transceiver is to be used selectively for different transmission power levels (e.g. by either activating all LED's or only half of them, depending on required range), a respective control signal can be furnished to transmitter stage 55 on an extra interface line 80. 45 Waveform samples of interface signals that are exchanged between the transceiver and the system unit (or I/O device, respectively) are shown in Fig. 6.

5.3 Circuit details for carrier sensing Carrier detector 47 and CS latch 53 serve to give an early warning of the presence of a transmission so (carrier sense delay time Td=1...5 microseconds depending on signal strength), and also serve to enable the Manchester decoder. (If the decoder were left enabled during idle periods, noise due to ambient light could occasionally cause wrong decoder outputs). Carrier sense filter (bandpass filter) 49 is tuned to the pulse frequency of the preamble that precedes each packet transmission. The output signal of the filter circuit is compared to a threshold amplitude value 55 in comparator 51 which changes its binary output signal only when the filter output exceeds the threshold, i.e. when it can be safely assumed that a carrier (and not only noise) is present (cf. Fig. 6). When the comparator output signal becomes active, it sets carrier sense latch (CS latch) 53 whose output signal CS is furnished on line 71 to the system unit for controlling the access protocol, and also to MDE 45 as enabling signal. CS latch 53 can only be reset by a respective signal "clear carrier sense" (CCS) on line 81 from the 60 processor of the system unit. Details of the use of carrier sense signal CS in the access protocol will be given in section 7. Carrier sense bandpass filter 49 can be embodied with operational amplifiers allowing a Q-factor of up to 15. An implementation using a ceramic filter is preferred because of higher Q's attainable and tighter tolerance of the center frequency. The carrier sense detection range (radius of C-boundary) should be as 65 close to the N-boundary as possible, so that the area where collisions can occur (carrier not clearly EP 0196 347 B1

detectable but above noise) is as small as possible. The relation depends on the bandpass Q-factor, carrier 4 sense delay, and preamble length. The range of zero interference (radius of N-boundary) is approximately times the D-range but depends heavily on orientation and ambient light level.

5 6. IR NETWORK packet format In the IR NETWORK, each data packet is preceded by a preamble and a start delimiter code violation and followed by an end delimiter code violation (see Fig. 3). It has fields for network control, addressing, data, and frame error control as described below and as shown in Fig. 7.

10 MODE: Eight bits. The mode field controls selective activation of units in the network. It comprises four "select" bits (7...4) and four "enable" bits (3...0). The group of normal devices, the repeater (or group of repeaters) and a possible gateway to another network are separately selectable by the select bits to be end-receivers of the frame. Just one of the select bits should be set in general. 15 DEV-SEL: Bit 7 (MSB). Selects all the devices, i.e. enables them to receive the frame and check the address field. This bit should be set to 1 for normal traffic on the IR network.

20 REP-SEL: Bit 6. Selects all repeaters. Should be set to zero for all but test and configuration traffic that addresses the enable bits the repeaters directly. The transparent repeater function () is controlled by described later.

25 GATW-SEL: Bit 5. Selects the gateway. Should be set to zero for normal traffic on the IR network. For traffic to a gateway DEV-SEL should be set to 0 and GATW-SEL set to 1.

30 (unused): .. Bit 4. To be set to zero in a pure IR system. In a mixed media system (IR and cable bound transmission), IR for this bit may be utilized to select the operating conditions for the medium used (zero for medium, one cable medium). To control the forwarding function of multiple repeaters, they can be enabled (activated) on a per frame REP3-EN 2), REP2-EN (Bit 1 ), 35 and per repeater basis by the four enable bits designated REP4-EN (Bit 3), (Bit and REP1-EN (Bit 0). Each of these bits enables one of four possible repeaters. The repeater enable bits should be set to zero in packets destined for local devices. For normal inter-workstation communication they should all be set to ones.

40 TO-ADDR: Eight bits. The TO-address field is the full network address of the destination device.

FROM-ADDR: , ...... 45 Eight bits. The FROM-address field is the full network address of the originating (sending) device. Both address fields are hierarchically structured into a STATION address and a DEVICE address sub-field:

STATION: . mIR so The station field contains the 5 most significant bits. This allows for a maximum of 32 stations on the network.

DEVICE: The device address is to be interpreted local to its workstation. The device field is in the three least 0 is 55 significant bits of the address byte. This allows for eight devices per workstation. Device address reserved for the keyboard. Device address 1 is the system unit.

DATA: 1 ...128 bytes. The data field might embed a higher level protocol. The data field is split into a one byte for 60 control field C and a variable length field I for data. Using HDLC elements of procedure allows a variety of protocol options.

CRC: 16 bits. The CRC field contains a 16-bit checksum. It covers the fields MODE, TO-ADDR, FROM-ADDR, 65 and the data field. EP 0196 347 B1

7. Access protocol Certain well known access protocols such as centralized polling or the token passing method are not feasible for the IR communication network described here.

s 7.1 Choice of protocol The proposed access mechanism is CSMA (Carrier Sense Multiple Access) for all stations capable of sensing the carrier. All other stations access the medium randomly (ALOHA) with an increased probability of collisions. High priority units (such as repeaters) have a first group of access slots assigned to them (which may be individually assigned as in slotted CSMA, or which may be used randomly by contention 10 between all high priority units). Lower priority units (such as I/O devices) content for the IR channel by random CSMA in a second group of slots that is assigned to them.

7.2 Transmission access delays Access delays are illustrated in Fig. 8. Afterthe end of a transmission follows the guard time interval Tg is during which receivers settle to the idle state. A new transmission may only be attempted after the guard time has elapsed. At the end of guard time Tg starts a sequence of 64 access slots each of duration Ts. Immediately following the guard time is one access slot (No. 1) for enabling start of a packet transmission acknowledging receipt of the previously transmitted data packet. Thereafter follows the first group of 20 access slots (Nos. 2...32) for the high priority units, which are in turn followed by the second group of access slots (Nos. 33...64) for the lower priority units. A device which is capable of detecting the end delimiter has to delay any attempt to transmit for the duration of the guard time Tg plus its individual access delay time Ta. A device within the C-boundary but outside the D-boundary of a sender, i.e. a device which cannot recognize the end of a packet transmission, 25 must delay any attempt to transmit for a time equivalent to the longest possible packet transmission Tpmax, plus guard time Tg, plus its individual access delay time Ta. The various time intervals are as follows:

Td=1...5 microseconds Carrier sense delay, depending 30 on signal amplitude and filter bandwidth

To ^Tpmax Time-out for maximum packet length

35 Tg=ca. 30... 300 microseconds Guard time, depending on receiving circuit

Ts=5 microseconds Access slot duration (Ts is of the same order as the carrier 40 sense delay time Td)

Ta=N * Ts Access delay

N=0 for acknowledgements 45 N=1...31 random number within these boundaries for high priority access

N=32...63 random number within these so boundaries for low priority access.

7.3 Finite state machine model of the infrared channel The IR channel can be in three different states, namely IDLE meaning that no infrared signal is present, 55 TRANSMIT meaning that infrared signals are present (emitted by one or several transmitters), and DEFER meaning that after the end of an infrared signal (a packet transmission) transceivers are waiting for individual predetermined intervals before they transmit. The latter state consists of two substates depending on the signal quality (i.e. end delimiter detected=good signal quality, or end delimiter not detected=bad signal quality). 60 Normally, the channel is in the IDLE state. Transitions between states occur after the following events: When the channel becomes active the IDLE state is left for the TRANSMIT state. After the end of a transmission the channel becomes inactive again and the state entered is now DEFER. As was mentioned, this state is divided into two substates depending on whether the end of a packet could be detected or not. In this state the stations wait for individual periods of time before transmitting again, or the channel returns es to IDLE if the access delays have expired and no station seized the opportunity to transmit.

8 EP 0196 347 B1

7.4 Definition of events and function states in the access protocol In the following there are defined all possible events and some of the function states (not to be mistaken for the IR channel states I, R, S, D) that may occur, and their effects on the access protocol. The access protocol is defined here in a formal way using the terminology of finite state machines. Based on 5 this formal description an implementation can be made either in hardware using gate-array technology or in software controlling a microprocessor. Reference is made to Fig. 8 which shows the protocol events for different situations.

* Carrier sense function states: 10 Let the Boolean function C(t) be defined as

after carrier was detected >■{:{1 0 after reset by an event EOG or EOPTO 15 The events EOG and EOPTO are defined later. The Boolean function C(t) is realized in carrier sense latch (CS latch) 53 which is triggered by the output signal of carrier detector 47 of the IR transceiver (Fig. 5). Thus, the function C(t) over time is equal to the waveform of signal CS shown in Fig. 6. The time delay Td is required for the detection operation and is in 20 the order of 5 microseconds maximum for a weak signal. Note that the analog carrier detector 47, due to its tuning to the packet preamble, only provides a trigger signal, not a continuous indication for the presence of a carrier.

* Event BOP (begin of packet): 25 This event is said to occur when C(t) undertakes a transition from 0 to 1. It signals the presence of a carrier in the IR channel. Note that the value C(t)=1 is stored in CS latch 53 even after the signal from the carrier sense filter 49 dropped below threshold.

* Event EOP (end of packet): . 30 This event is said to occur when the end delimiter of a packet has been detected. End delimiter detection is integrated into the Manchester decoder/encoder 45, and the respective signal indication is the event available on line 69. Instead of using hardware end delimiter detection, the packet end (and thus EOP) could also be detected by software when the CRC check is successfully completed. time The occurrence of this event is taken as the first priority time base to synchronize access delay 35 Slots.

* Event EOG (end of guard time): This event is said to occur when a time-out ends which is started at event EOP and which lasts for the duration of the guard time Tg. 40 * Event EOPTO (end of packet time-out): This event is said to occur when the receiving station was unable to detect the end of a packet due to a This collision or due to a poor signal/noise ratio causing the receiver PLL to loose synchronization. event the occurs on time-out of a counter loaded with a deJay time "To" where To^Tpmax, Tpmax being 45 maximum packet length. The occurrence of this event is taken as the second priority time base to synchronize access delay time slots.

* Event SDEL (start delimiter detected): when the so This event is said to occur when the start delimiter is detected. It is captured output signal NVM of Manchester decoder/encoder 45 goes from 0 to 1.

* Event EOAD (end of access delay): This event is said to occur on time-out of a counter loaded with the individually calculated access delay 55 time "Ta". * Transmission buffer function states: The state of the transmit buffer which is provided in each unit or device is defined as follows:

60 f 1 if transmit buffer at time t is not empty TB(t)=4 10 if transmit buffer at time t is empty.

The value of this function is stored in a transmit buffer state latch whose binary output value can be ss regarded as a transmit request signal to the access logic. EP 0196 347 B1

* Event EOADTX (transmit after end of access delay): This event is said to occur when the access delay time Ta has expired and the transmit buffer of the respective unit was not empty.

5 * Event TX (frame to transmit): This event is said to occur when the channel is idle and a transition of TB(t) from 0 to 1 is taking place.

* Event FTX (forced transmit): This event is said to occur when a station with high transmit priority (such as a keyboard) is ignoring 10 the busy channel and enforces the transmission of a packet. Because of the characteristics of the IR channel and the receiver circuitry, and the close proximity of the two involved devices (system unit with allocated keyboard) resulting in a strong signal for the receiving device, it is likely that the packet is received correctly (capturing the channel). This event may be triggered by a time-out condition in the respective device. 15 7.5 Mechanism of access protocol In the following, a description is given of the possible state transitions that can occur as seen from a single transceiver. The state diagram as seen from a transceiver point-of-view is shown in Fig. 9. Note that the "transmit" state (that was defined for the IR channel) is now split up into two different states "R" and 20 "S" depending on whether the particular transceiver is either listening/receiving or sending. The time sequence of events is shown in Fig. 8, and a flowchart representation of the access protocol is given in Fig. 10. Assume that the transceiver is in the idle state "I". If the carrier detector 47 responds to a preamble by setting CS latch 53, indicating the value of the Boolean carrier sense function to be C(t)=1, the idle state is 25 left for the receiving state "R". This represents the begin of a packet, BOP. At this time a counter is also loaded with a To count (To=Tpmax). Note that for the length of the interval during which C(t)=1, Manchester decoder/encoder 45 remains enabled. CS latch 53 will only be reset when the end of a packet (EOP) is indicated, thus serving as a new time reference for synchronizing the access slots, or when a time-out EOPTO occurs. 30 The receive state "R" can be left for the defer state "D" (either D1 or D2) in two different situations: If the received signal quality (signal-to-noise ratio) is good the Manchester decoder 45 will acquire synchronization after the preamble and start delimiter. This event SDEL will reload a timing counter with the time-out To. The detection of the end of the packet (EOP) will serve as a new time reference for synchronizing the access slots. The receive state "R" is now left for the defer state D1 and a counter is 35 loaded with the guard time Tg. If the received signal quality is poor (between D-boundary and C-boundary, cf. Fig. 4), Manchester decoder 45 may not acquire synchronization or will loose it and may not be able to detect the end of the packet (EOP). In this case the receive state can only be left when the time-out EOPTO occurs. The new time reference is the time-out EOPTO. Note that while the receiving or listening transceiver is in the receive state 40 "R" the detection of a new start delimiter (SDEL) will reload a counter with the time-out value To and keep the Manchester encoder enabled for at least one other maximum packet length. This mechanism prevents that the Manchester decoder becomes disabled due to a time-out condition when in progress of receiving a subsequent packet. For devices requiring fast access times such as keyboards, joysticks, or touch panels a forced transmit 45 mode FTX is provided. If these devices have to wait too long for a chance to transmit a packet due to a heavily loaded channel, a time-out in a higher level protocol layer can force an exit from the receiving state "R" directly to the send state "S". This option is reserved for pairs of groups of terminals located closely together and having a low LED optical power rating. Due to the close distance the resulting signal-to-noise ratio is high and the chance of capturing the channel in the presence of another packet is also high, even so without causing destructive interference at the receiving station of the other packet (if it is not just one of the closely located terminals). On entering the defer state "D" (D1) via the EOP event a counter is loaded with the guard time Tg and after time-out, CS latch 53 is reset. This disables the Manchester decoder and renders the CS latch ready for a new carrier sense trigger pulse. At time-out of Tg a counter is loaded with the calculated delay count Ta. 55 On entering the defer state "D" (D2) via the EOPTO event CS latch 53 is reset immediately and the guard time count Tg is loaded. This procedure gives the carrier detector more time to respond to the pressure of a carrier. Note that in this situation a transmission may be already in progress and the carrier detector has to respond to the Manchester coded data and not to the preamble signal to which the carrier sense bandpass filter 49 is tuned. The spectral energy matching the carrier sense filter is highest for a 60 preamble (as defined in section 2.1), and least for the data bit sequence 10101010.... Hence the response time for the carrier detector depends on the current data pattern and may be longer than for detecting a preamble directly. For this purpose the CS latch is reset at the EOPTO event already, giving the carrier detector more time to respond. After this time procedure for the access delay is the same as for the EOP event. 65 If during the access delay, i.e. before the time-out of Ta occurs, a carrier is sensed, CS latch 53 is set

10 EP 0196 347 B1 If the again, and this event BOP causes a transition from defer state "D" back to receiving state "R". time-out of Ta occurs before a new carrier preamble is sensed, the following two steps are possible: The defer state "D" is left for the idle state "I" after the access delay has expired, if the transmit buffer was empty (EOAD). On the other hand, the defer state is left for the send state "S" when the access delay s expired and the transmit buffer was not empty (EOADTX). A transition to the send state "S" can occur in two different situations. One was just mentioned, i.e. if in the defer state the access delay expires and the transmit buffer is not empty (TB(t)=1 ). The other situation is if in the idle state "I" the transmit buffer receives data, i.e. if TB(t) goes from 0 to 1 (event TX). There is no exit from the send state "S" until the transmission is completed (event EOP). (It is not IR echo reflected w possible for the transmitting station to detect a collision reliably, because of the strong back into the receiver of the transmitting device). After completion of the transmission the sending station back to the defer state and only from there to the idle state. goes With reference to Fig. 10 represents a flowchart of the basic protocol procedure described above. sections 7.2, 7.4, and 7.5 it is self-explaining and therefore needs no further description. 15 7.6 Logic circuitry for access protocol I/O device. Fig. 11 shows a block diagram of logic circuitry that can be provided in a system unit or an of for handling the access protocol. The logic circuitry uses as input signals various output signals Manchester decoder (MDE) 45 and CS latch 53 which are parts of the transceiver but which are also shown 20 in Fig. 11, as well as the TB(t) signal of a transmit buffer state latch 85, and a signal "high local priority time-out" that is provided on line 87 e.g. in keyboards and other devices that must be served promptly but have low transmission power. ,^«ArvTV This access protocol logic circuitry furnishes three different transmission enabling signls (EOADTX, TX, FTX) to transmission control circuitry 89 that is provided in the respective device. the flow chart of 10 25 The whole arrangement shown in Fig. 11 is self-explaining with reference to Fig. and to the description given in subsections 7.2, 7.4, and in particular in subsection 7.5. In the logic circuitry of Fig. 11 four time-out or delay counters 93, 95, 97, 99 are shown for enabling different delays To, Ta, and Tg, respectively. Instead of providing the four counters as shown (which are never used simultaneously) one could of of 30 course use only a single counter plus additional multiplexing or gating circuitry so that upon occurrence of the a particular start signal the correct time-out value (To, Ta, Tg) is loaded, and upon occurrence time-out the respective pulse is furnished to the correct AND or OR gate.

7.7 Collision avoidance and carrier enforce bursts collision at third 35 Two transceivers that are not within each other's C-boundary can cause an access a station. In this case the CSMA protocol degrades to an ALOHA-type access protocol. Weak devices local to transmitters a workstation suffer most from this situation. The problem can be alleviated by having the of the sender to emit a strong carrier burst preceding a low power data frame. This extends the C-boundary its N-boundary. involves 40 An additional mechanism that reduces access collisions by enforcing proper carrier sensing, duration Tb 8, repeaters. When a repeater encounters a preamble it transmits a short burst carrier of (Fig. top left). So, the device's transmission preamble gets sensed not just within the transmitter's C-boundary but even within the much larger C-boundary of the repeater. This prevents stations from gaining interfering allow the access. However, if carrier enforce bursts are provided the preamble must be sufficiently long to before the end of the preamble, to 45 carrier enforce burst signal to decay to the normal received signal level ensure proper decoding of the subsequent data stream. 7.8 Modification for cable-bound transmission In a mixed media system, the access method described in this section and the packet format described cable-bound medium, with the following 50 in the preceding section can also be used for transmissions on the exceptions: The features carrier sense burst, repeater enabling, and different LED transmitter power levels are disabled by setting bit 4 of the MODE control bits to one.

8. Repeaters the overall transmission or to 55 At least one repeater can be added to the network to increase range provide multiple and spatially diverse signal paths to "hidden stations" in a difficult environment (cf. Fig. 1C). It provides a datagram service, i.e. it repeats remote traffic on a best effort basis without invoking the data link layer (error corrections). In order to avoid overloading the network with repeater traffic the maximum number of repeaters should be limited to four. and exclude delayed arrival of packets with so To avoid unnecessary circulation of duplicate packets to ambiguous sequence numbers when using the IBM SDLC (Synchronous Data Link Control) protocol, repeaters have to adhere to the following rules: * Each repeater can buffer only one packet of maximum length. * Incoming packets are discarded if the buffer is not free. enable bit bit) is not set. 65 * A repeater discards a frame if its (REPx-EN

11 EP 0196 347 B1

* A sending station can enable specific repeaters. Normally, all installed repeaters are to be enabled. Hence, all repeaters support forwarding this frame and the packet is receivable at all stations on the IR network. If all repeater enable bits are zero no repeater forwards the frame. This is intended for traffic local to a station. s * A repeater discards a frame received with incorrect checksum. * A repeater keeps the checksum of the last frame transmitted for a given time interval. During that time interval it discards all newly arriving frames having an identical checksum. * If access to the IR channel is not granted to the repeater within the period of 4 maximum length frames, then the packet is discarded. JO

Claims

1. System for interconnecting a plurality of data transmitting and/or receiving units (11, 13, 15, 17, 23) 15 by infrared signals, said units including a plurality of stations (11) and associated I/O devices (13, 15), each said unit comprising at least one infrared transceiver (31, 33, 35) and accessing the common infrared communication channel only in dependence of a carrier sense function, characterized in that — said transceivers (31, 33, 35) are adapted to be assigned to one of a plurality of hierarchical categories reflecting their required distance range of coverage, and that infrared transmitting power and/or 20 receiving sensitivity of the transceivers of each category have a given magnitude different from those of the other categories. 2. A system according to claim 1, characterized in that at least one repeater unit (17, 19, 21) is provided for retransmitting received data packets to increase the covered distance range, and that the transceivers of all repeater units are assigned to the category having the highest transmitting power and receiving 25 sensitivity. 3. A system according to claim 1 or 2, characterized in that the transceivers (31 , 33, 35) of each category have a specific number of light emitting diodes and a specific number of photodiodes thus determining the transmitting power and receiving sensitivity, respectively, of each transceiver of the respective category. 4. A system according to claim 1 or 2, characterized in that in at least one of said transceivers (31, 33, 30 35), one of plural different magnitudes of transmitting power and/or receiving sensitivity can be selected by a respective control signal (80). 5. A system according to claim 1, characterized in that each unit comprises means for transmitting, after getting access to the infrared channel, a preamble of given duration (Tor), consisting of a sequence of rectangular pulses representing the infrared carrier signal, prior to transmitting the data (Fig. 3; Fig. 6). 35 6. A system according to claims 2 and 5, characterized in that each repeater comprises means for transmitting a short carrier enforce burst of a duration (Tb) shorter than the preamble duration (Tpr), after detecting a preamble signal (Fig. 8). 7. A system according to claim 1, characterized in that each said unit (11, 13, 15, 17) comprises means for transmitting data in frames in the form of packets comprising a data field, at least one address field, and 40 a control field comprising mode bits for selectively enabling units receiving a respective packet (Fig. 7). 8. A system according to claim 1, characterized in that each unit comprises means (47, 53, 89) for inhibiting transmission as soon as an infrared carrier preamble or data signal is detected; means (93) for starting a first time-out cycle of given duration (To) when a carrier preamble or data signal is detected (BOP); means (45) for detecting an end-of-transmission indication (EOP); means (95) for starting a second 45 time-out cycle of a duration (Ta) individual to the respective unit either after detection of an end-of-transmission indication (EOP) or after the end of the first time-out cycle (EOPTO); and means (53, 89) for enabling a transmission in response to the end indication of said second time-out cycle (EOAD) if no infrared carrier preamble or data signal was received in the meantime. 9. A system according to claim 8, characterized in that additional means (97, 99) are provided in each so unit for starting a third time-out cycle (Tg) immediately either at the end of said first time-out cycle (EOPTO) or upon detection of an end-of-transmission indication (EOP), and that said means (95) for starting the second time-out cycle (Ta) is responsive to an end indication (EOG) of said third time-out cycle, so that in each unit a guard time (Tg) is obtained during which no transmission is possible. 10. A system in accordance with claim 1, characterized in that at least one (23) of said data transmitting 55 and/or receiving units is connected to a communication subnetwork in which data are transferred via electrical or optical cable to and from at least one other data transmitting and/or receiving unit. 1 1 . A system in accordance with claim 1 , characterized in that at least one (23) of said data transmitting and receiving units comprises transceiver means connecting it to a subnetwork including other data transmitting and/or receiving units which are interconnected by electrical or optical cables, and that each of 60 said units interconnected by infrared signals and each of said other units interconnected by cables, comprises means (47, 53, 89) for inhibiting transmission as soon as carrier preamble or data signal is detected; means (93) for starting a first time-out cycle of given duration (To) when a carrier preamble or data signal is detected (BOP); means (45) for detecting an end-of-transmission indication (EOP); means (95) for starting a second time-out cycle of a duration (Ta) individual to the respective unit either after detection 65 of an end-of-transmission indication (EOP) or after the end of the first time-out cycle (EOPTO); and means

12 EP 0196 347 B1

(53, 89) for enabling a transmission in response to the end indication of said second time-out cycle (EOAD) if no carrier preamble or data signal was received in the meantime. 12. Method of transmitting data signals in a system comprising a plurality of units including stations and devices assigned to said stations, in which system any unit accesses a common transmission medium in 5 only in dependence of a carrier sense function for transmitting data in the form of packets, characterized that — each unit, when its receiver senses a signal transmission, enters a non-transmit state and starts a time-out cycle of a duration (To) at least equal to the longest packet transmission time (Tpmax), and that — either upon detection of an end-of-transmission delimiter (EOP) or upon end of the time-out cycle io (EOPTO), each said unit during a sequence of time slots, starts any data transmission only in a time slot assigned to it, if it did not detect a signal transmission in the meantime. 13. Method of transmitting data by infrared signals in a system comprising a plurality of units including stations and devices assigned to said stations, in which system any unit accesses the common infrared transmission channel only in dependence of a carrier sense function for transmitting data in the form of 75 packets, characterized in that — transmitters and receivers (31, 33, 35) of all units are operated with different transmitting powers and receiving sensitivities depending on the required distance range to be covered, — each unit, when its receiver senses an infrared signal transmission, enters a non-transmit state and starts a time-out cycle of a duration (To) at least equal to the longest possible packet transmission time 20 (Tpmax), and that either upon detection of an end-of-transmission delimiter (EOP) or upon end of the time-out cycle (EOPTO), each said unit during a sequence of time slots, starts any data transmission only in a time slot assigned to it, if it did not detect an infrared signal transmission in the meantime. 14. A method according to claim 13, characterized in that a transmitter of any unit getting access to the 25 infrared channel first transmits a preamble of rectangular pulses representing the carrier of the infrared signal prior to transmitting a data packet. 15. A method according to claim 14, characterized in that the preamble is transmitted at higher signal power than the subsequent data. 16. A method according to claim 13, characterized in that the data packets are transmitted in the form of 30 frames and that each frame includes a control field comprising mode bits for selectively activating units. 17. A method according to claim 13, characterized in that upon detection of an end-of-transmission delimiter (EOP) or upon indication of the end of the time-out cycle (EOPTO), each said unit starts a second time-out cycle representing a guard time (Tg) to allow all receivers to settle to equilibrium, and that upon an end indication of the second time-out cycle (EOG) a third time-out cycle is started of a duration (Ta) which is unit 35 individually selected in the respective unit, and that the non-transmit state is left for the respective upon occurrence of an indication of the end (EOAD) of the third time-out cycle. 18. A method according to claim 13, characterized in that each of said units, when it transmitted a data packet of given duration (Tp), inhibits any data transmission for a period at least equal to said transmitted packet duration (Tp), thus reducing the duty cycle of its transmitter to a fraction of the total possible 40 transmission time to allow cooling of light emitting diodes between transmissions. 19. A system for interconnecting data transmitting and receiving units including a plurality of stations (11) and associated I/O devices (13, 15) and at least one repeater unit (17), by infrared signals, information being transmitted in the form of packet frames comprising at least one address field and a control information field, characterized in that 45 — means are provided in each said unit for activating the respective unit to accept or to retransmit a received packet frame only if that unit is selected by an assigned mode control bit in the respective frame, said control information field comprising mode control bits each for selecting one of said units individually or for selecting a group of said units having the same function in the system. 20. A system according to claim 19, characterized in that each said unit (11, 13, 15, 17) comprises at of limited number of so least one infrared transceiver (31 , 33, 35), and that each transceiver belongs to one a hierarchical categories each having different transmitting power and receiving sensitivity, according to the required distance covering range of the transceivers of the respective category.

Patentanspriiche

1. System zur Verbindung einer Mehrzahl von Daten sendenden und/oder empfangenden Einheiten (11, 13, 15, 17, 23) durch Infrarot-Signale, wobei zu den Einheiten eine Mehrzahl von Stationen (11) und zugehorige Eingabe/Ausgabe-Einheiten (13, 15) gehoren, und wobei jede der Einheiten mindestens einen Infrarot-Sender/Empfanger (31, 33, 35) enthalt und zu dem Infrarot-Kanal nur in Abhangigkeit von einer 60 Tragerdetektor-Funktion zugreift, dadurch gekennzeichnet, dass — die Sender/Em pf anger (31, 33, 35) so eingerichtet sind, dass sie einer von mehreren hierarchischen Kategorien zugeordnet werden konnen, welche den erforderlichen Reichweiten entsprechen, und dass die Infrarot-Sendeleistung und/oder -Empfangsempfindlichkeit der Sender/Empfanger jeder Kategorie eine bestimmte Grosse haben, welche sich von denen der anderen Kategorien unterscheidet. eine Relaiseinheit(17, 19,21) 65 2. System gemass Anspruch 1, dadurch gekennzeichnet, dass wenigstens

13 EP 0196 347 B1

vorhanden ist zur Weitersendung empfangener Datenpakete, urn die erreichbare Reichweite zu vergrossem, und dass die Sender/Empfanger aller Relaiseinheiten derjenigen Kategorie zugeordnet sind, welche die grosste Sendeleistung und Empfangsempfindlichkeit hat. 3. System gemass Anspruch 1 oder 2, dadurch gekennzeichnet, dass die Sender/Empfanger (31 , 33, 35) 5 einer jeden Kategorie eine bestimmte Anzahl von Leuchtdioden und eine bestimmte Anzahl von Photodioden aufweisen, wodurch die Sendeleistung und die Empfangsempfindlichkeit jedes Sender/ Empfangers der betreffenden Kategorie bestimmt werden. 4. System gemass Anspruch 1 oder 2, dadurch gekennzeichnet, dass in wenigstens einem der Sender/Empfanger (31, 33, 35) eine von mehreren verschiedenen Grossen der Sendeleistung und/oder 10 Empfangsempfindlichkeit durch ein entsprechendes Steuersignal (80) ausgewahlt werden kann. 5. System gemass Anspruch 1, dadurch gekennzeichnet, dass jede Einheit Einrichtungen enthalt urn, nach Erlangung des Zugriffs zum Infrarot-Kanal und vor der Aussendung von Daten, eine Praambel vorgegebener Zeitdauer (Tpr) auszusenden, welche aus einer Folge von Rechteckimpulsen besteht, die das Infrarot-Tragersignal darstellen (Fig. 3; Fig. 6). 15 6. System gemass Anspruch 2 und 5, dadurch gekennzeichnet, dass jede Relaiseinheit Einrichtungen enthalt, urn nach Detektierung eines Praambelsignals einen kurzen Tragersignal-Verstarkungsstoss auszusenden, dessen Dauer (Tb) kleiner ist als die Dauer (Tpr) der Praambel (Fig. 8). 7. System gemass Anspruch 1, dadurch gekennzeichnet, dass jede Einheit (11, 13, 15, 17) Einrichtungen enthalt, urn Daten in Rahmen in der Form von Paketen auszusenden, welche ein Datenfeld, 20 wenigstens ein Adressfeld und ein Steuerfeld umfassen, zu dem Modus-Bits gehoren, durch welche Einheiten, welche ein entsprechendes Paket empfangen, selektiv aktiviert werden konnen (Fig. 7). 8. System gemass Anspruch 1, dadurch gekennzeichnet, dass jede Einheit Einrichtungen (47, 53, 89) enthalt, um eine Aussendung zu unterbinden, sobalt ein Infrarot-Tragersignal oder ein Datensignal detektiert wird; weiterhin Einrichtungen (93) zum Starten eines ersten Wartezeit-lntervalls vorgegebener 25 Dauer (To), wenn eine Trager-Praambel oder ein Datensignal detektiert wird (BOP); Einrichtungen (45) zur Detektierung einer Sendeschluss-Anzeige (EOP); Einrichtungen (95) zum Starten eines zweiten Wartezeit- lntervalls vorgegebener Dauer (Ta), welche der betreffenden Einheit individuell zugeordnet ist, und zwar entweder nach der Detektierung einer Sendeschluss-Anzeige (EOP) oder nach Beendigung des ersten Wartezeit-lntervalls (EOPTO); und Einrichtungen (53, 89), um eine Aussendung zu ermoglichen aufgrund 30 der Beendigung des zweiten Wartezeit-lntervalls (EOAD), falls in der Zwischenzeit keine Infrarot-Trager- praambel und kein Datensignal empfangen wurden. 9. System gemass Anspruch 8, dadurch gekennzeichnet, dass in jeder Einheit weitere Einrichtungen (97, 99) vorhanden sind, um ein drittes Wartezeit-lntervall (Tg) zu starten entweder unmittelbar nach dem Ende des ersten Wartezeit-lntervalls (EOPTO) oder nach Detektierung einer Sendeschluss-Anzeige (EOP), 35 und dass die Einrichtungen (95) zum Starten des zweiten Wartezeit-lntervalls (Ta) ansprechen auf eine Endanzeige (EOG) des dritten Wartezeit-lntervalls, so dass in jeder Einheit eine Schutzzeit (Tg) eingehalten wird, wahrend derer keine Aussendung moglich ist. 10. System gemass Anspruch 1, dadurch gekennzeichnet, dass wenigstens eine (23) der Daten aussendenden und/oder empfangenden Einheiten mit einem Nachrichten-Untemetzwerk verbunden ist, in 40 dem Daten durch elektrische oder optische Kabel zu oder von wenigstens einer weiteren Daten aussendenden und/oder empfangenden Einheit ubertragen werden. 11. System gemass Anspruch 1, dadurch gekennzeichnet, dass wenigstens eine (23) der Daten aussendenden und empfangenden Einheiten Sender/Empfanger-Einrichtungen enthalt, welche sie mit einem Untemetzwerk verbinden, das andere Daten aussendende und/oder empfangende Einheiten 45 umfasst, die durch elektrische oder optische Kabel miteinander verbunden sind, und dass jede der Einheiten, die durch Infrarot-Signale miteinander verbunden sind sowie jede der anderen Einheiten, die durch Kabel miteinander verbunden sind, Einrichtungen (47, 53, 89) enthalt, um eine Aussendung zu unterbinden, sobald eineTragerpraambel oder ein Datensignal detektiert werden; weiterhin Einrichtungen (93) zum Starten eines ersten Wartezeit-lntervalls vorgegebener Dauer (To), wenn eine Trager-Praambel so oder ein Datensignal detektiert werden (BOP); Einrichtungen (45) zur Detektierung einer Sendeschluss- Anzeige (EOP); Einrichtungen (95) zum Starten eines zweiten Wartezeit-lntervalls vorgegebener Dauer (Ta), welche der betreffenden Einheit individuell zugeordnet ist, und zwar entweder nach der Detektierung einer Sendeschluss-Anzeige (EOP) oder nach Beendigung des ersten Wartezeit-lntervalls (EOPTO); und Einrichtungen (53, 89); um eine Aussendung zu ermoglichen aufgrund der Endanzeige des zweiten 55 Wartezeit-lntervalls (EOAD), wenn in der Zwischenzeit keine Tragerpraambel und kein Datensignal empfangen wurden. 12. Verfahren zur Ubertragung von Datensignalen in einem System, welches eine Mehrzahl von Einheiten enthait, wozu Stationen und diesen Statiqnen zugeordnete Gerate gehoren, und in welchem System irgendeine Einheit zu einem gemeinsamen Gbertragungsmedium zur Aussendung von Daten in 6Q Form von Paketen nur aufgrund einer Tragerdetektorfunktion zugreifen kann, dadurch gekennzeichnet, dass — jede Einheit dann, wenn ihr Empfanger eine Signalubertragung feststellt, in einen Nichtsende- Zustand eintritt und ein Wartezeit-lntervall startet von einer Dauer (To), welche mindestens gleich der langsten Paket-Ubertragungszeit (Tpmax) ist, und dass 6S — entweder nach Detektierung eines Sendeschluss-Begrenzers (EOP) oder bei Beendigung des

14 EP 0196 347 B1

Wartezeit-lntervalls (EOPTO) jede der Einheiten eine Folge von Zeitschlitzen startet und eine Datenubertragung nur in einem ihr zugeordneten Zeitschlitz beginnt, sofern sie nicht in der Zwischenzeit eine Signalubertragung detektiert hat. eine 13. Verfahren zur Ubertragung von Daten mittels infraroter Signale in einem System, welches und in 5 Mehrzahl von Einheiten enthalt, wozu Stationen und diesen Stationen zugeordnete Gerate gehdren, welchem System irgendeine Einheit zu einem gemeinsamen Infrarot-Ubertrgungskanal zur Aussendung dadurch von Daten in Form von Paketen nur aufgrund einer Tragerdetektorfunktion zugreifen kann, gekennzeichnet, dass . und — Sender und Empfanger (31, 33, 35) aller Einheiten mit unterschiedhchen Sendeleistungen 10 Empfangsempfindlichkeiten betrieben werden, welche von der erforderlichen Reichweite abhangen, in einen — jede Einheit dann, wenn ihr Empfanger eine Infrarot- Signalubertragung feststellt, Nichtsende-Zustand eintritt und ein Wartezeit-lntervall startet von einer Dauer (To), welche mindestens der langsten Paket-Ubertragungszeit (Tpmax) ist, und dass gleich des — entweder nach Detektierung eines Sendeschluss-Begrenzers (EOP) oder bei Beendigung eine 15 Wartezeit-lntervalls (EOPTO) jede der Einheiten wahrend einer Folge von Zeitschlitzen Zwischenzeit Datenubertragung nur in einem ihr zugeordneten Zeitschlitz beginnt, sofern sie nicht in der eine Infrarot-Signalubertragung detektiert hat. _ welche 14. Verfahren gemass Anspruch 13, dadurch gekennzeichnet, dass ein Sender einer Einheit, Zugriff zum Infrarot-Kanal erreicht, zuerst eine Praambel rechteckiger Impulse, welche den Infrarot-Trager 20 darstellen, aussendet, bevor sie ein Datenpaket aussendet. mit 15. Verfahren gemass Anspruch 14, dadurch gekennzeichnet, dass die Praambel grosserer Signalenergie ausgesendet wird als die nachfolgenden Daten. in der Form 16. Verfahren gemass Anspruch 13, dadurch gekennzeichnet, dass die Datenpakete von selektiven Rahmen ubertragen werden, und dass jeder Rahmen ein Steuerfeld enthalt mit Modus-Bits zur 25 Aktivierung von Einheiten. 17 Verfahren Anspruch 13, dadurch gekennzeichnet, dass bei Detektierung eines gemass ein Sendeschluss-Begrenzers (EOP) oder am Ende des Wartezeit-lntervalls (EOPTO) jede der Einheiten zweites Wartezeit-lntervall startet, welches eine Schutzzeit (Tg) darstellt, urn den Empfangern eine Ruckkehr in einen Ruhezustand zu ermdglichen,- und dass aufgrund einer Endanzeige des zweiten welche fur die 30 Wartezeit-lntervalls (EOG) ein drittes Wartezeit-lntervall gestartet wird von einer Dauer (Ta), betreffende Einheit individuell ausgewahlt ist, und dass der Nichtsende-Zustand in der betreffenden Einheit verlassen wird beim Auftreten einer Endanzeige (EOAD) fur das dritte Wartezeit-lntervall. 18. Verfahren gemass Anspruch 13, dadurch gekennzeichnet, dass jede der Einheiten, wenn sie em Datenpaket vorgegebener Lange (Tp) ubertragen hat, jegliche Datenubertragung fur eine Zeitdauer dadurch den 35 unterbindet, welche mindestens der ubertragenen Paketdauer (Tp) entspricht, urn Arbeitszyklus ihres Senders auf einen Bruchteil der total moglichen Sendezeit zu beschranken, urn so eine Abkuhlung der Leuchtdioden zwischen den Ubertragungen zu ermdglichen. Mehrzahl 19. System zur Verbindung von Daten sendenden und empfangenden Einheiten, wozu eine eine von Stationen (11) mit zugeordneten Eingabe/Ausgabe-Einheiten (13, 15) und mindestens Relaiseinheit (17) gehdren, durch Infrarot-Signale, wobei die Information in der Form von Paketrahmen 40 dadurch ubertragen wird, welche wenigstens ein Adressfeld und ein Steuerinformationsfeld enthalten gekennzeichnet, dass — in jeder Einheit Einrichtungen vorhanden sind, urn die betreffende Einheit zur Annahme Oder zur Weiterubertragung eines empfangenen Paketes nur dann zu aktivieren, wenn diese Einheit durch ein wurde, wobei das 45 zugeordnetes Modus-Steuerbit in dem betreffenden Rahmen ausgewahlt Steuerinformationsfeld Modus-Steuerbits enthalt, deren jedes eine der Einheiten individuell auswahlt oder eine Gruppe von Einheiten, welche die gleiche Funktion im System ausiiben. 17) 20. System gemass Anspruch 19, dadurch gekennzeichnet, dass jede Einheit (11, 13, 15, mindestens einen Infrarot-Sender/Empfanger (31, 33, 35) enthalt, und dass jeder Sender/Empfanger zu einer Kategorie einer begrenzten Anzahl von hierarchischen Kategorien gehort, die jede eine andere SO Sender/ Sendeleistung und Empfangsempfindlichkeit haben, gemass der erforderlichen Reichweite der Empfanger der betreffenden Kategorie. Revendications de donnees (11, 1. Systeme pour interconnecter une pluralite de modules d'emission et/ou reception de 13, 15, 17, 23) par des signaux infrarouges, les modules comprenant une pluralite de stations (11) et dispos'itifs d'entree/sortie E/S associes (13, 15), chaque module comprenant au moins un emetteur- recepteur infrarouge (31, 33, 35) et accedant au canal de communication infrarouge courant seulement caracterise ce bo sous la dependance d'une fonction de detection de porteuse, en que — les emetteurs-recepteurs (31, 33, 35) sont adaptes a etre affectes a I'une d'une pluralite de categories hierarchiques refletant leur domaine de distance requise de couverture, et en ce que la puissance d'emission et/ou la sensibilite de reception des emetteurs-recepteurs de chaque categorie ont une grandeur donnee differente de celles des autres categories. caracterise moins un module repeteur (17, 19, 21) est 65 2. Systeme selon la revendication 1 , en ce qu'au

15 EP 0196 347 B1

prevu pour reemettre des paquets de donnees regus pour augmenter le domaine de distance couvert, et en ce que les emetteurs-recepteurs de tous les modules repeteurs sont affectes a la categorie ayant la puissance d'emission et la sensibilite de reception les plus hautes. 3. Systeme selon Tune des revendications 1 ou 2, caracterise en ce que les emetteurs-recepteurs (31, s 33, 35) de chaque categorie ont un nombre specifique de diodes emettrices de lumiere et un nombre specifique de photodiodes determinant ainsi la puissance d'emission et la sensibilite de reception, respectivement, de chaque emetteur-recepteur de la categorie respective. 4. Systeme selon I'une des revendications 1 ou 2, caracterise en ce que dans au moins I'un des emetteurs-recepteurs (31,33, 35), une parmi plusieurs grandeurs differentes de puissance d'emission et/ou 10 de sensibilite de reception peut etre choisie par un signal de commande respectif (80). 5. Systeme selon la revendication 1 , caracterise en ce que chaque module comprend des moyens pour emettre, apres I'obtention de I'acces au canal infrarouge, un preambule de duree donnee (Tpr), consistant en une sequence d'impulsions rectangulaires representant le signal de porteuse infrarouge, avant d'emettre les donnees (figure 3; figure 6). is 6. Systeme selon les revendications 2 et 5, caracterise en ce que chaque repeteur comprend des moyens pour emettre une breve salve de renforcement de porteuse d'une duree (Tb) inferieure a la duree (Tpr) du preambule, apres la detection d'un signal de preambule (figure 8). 7. Systeme selon la revendication 1, caracterise en ce que chaque module (11, 13, 15, 17) comprend des moyens pour emettre les donnees en trames sous la forme de paquets comprenant un champ de donnees, 20 au moins un champ d'adresses, et un champ de commande comprenant des bits de mode pour valider de fagon selective les modules recevant un paquet respectif (figure 7). 8. Systeme selon la revendication 1, caracterise en ce que chaque module comprend des moyens (47, 53, 89) pour inhiber remission aussitot qu'un preambule de porteuse ou un signal de donnees infrarouge est detecte; des moyens (93) pour commencer un premier cycle d'attente d'une duree donnee (To) quand 25 un preambule de porteuse ou un signal de donnees est detecte (BOP); des moyens (45) pour detecter une indication de fin d'emission (EOP); des moyens (95) pour commencer un second cycle d'attente d'une duree (Ta) propre au module respectif apres la detection d'une indication de fin d'emission (EOP) ou bien apres la fin du premier cycle d'attente (EOPTO); et des moyens (53, 89) pour valider une emission en reponse a I'indication de fin du second cycle d'attente (EOAD) si aucun preambule de porteuse ou signal de 30 donnees infrarouge n'a ete regu pendant ce temps-la. 9. Systeme selon la revendication 8, caracterise en ce que des moyens supplementaires (97, 99) sont prevus dans chaque module pour commencer un troisieme cycle d'attente (Tg) immediatement a la fin du premier cycle d'attente (EOPTO) ou bien a la suite de la detection d'une indication de fin d'emission (EOP), et en ce que les moyens (95) pour commencer le second cycle d'attente (Ta) repondent a une indication de 35 fin (EOG) du troisieme cycle d'attente, de telle fagon que dans chaque module un temps de garde (Tg) soit obtenu pendant lequel aucune emission n'est possible. 10. Systeme selon la revendication 1, caracterise en ce qu'au moins I'un (23) des modules d'emission et/ou reception de donnees est connecte a un sous-reseau de communication dans lequel les donnees sont transferees par I'intermediaire de cables electriques ou optiques en direction et a partir d'au moins un autre 40 module d'emission et/ou reception de donnees. 11. Systeme selon la revendication 1, caracterise en ce qu'au moins I'un (23) des modules d'emission et/ou reception de donnees comprend des moyens emetteurs-recepteurs le connectant a un sous-reseau comprenant d'autres modules d'emission et/ou reception de donnees qui sont interconnectes par des cables electriques ou optiques, et en ce que chacun des modules interconnectes par signaux infrarouges et 45 chacun des autres modules interconnectes par cables comprennent des moyens (47, 53, 89) pour inhiber remission aussitot qu'un preambule de porteuse ou un signal de donnees est detecte; des moyens (93) pour commencer un premier cycle d'attente d'une duree donnee (To) quand un preambule de porteuse ou un signal de donnees est detecte (BOP); des moyens (45) pour detecter une indication de fin d'emission (EOP); des moyens (95) pour commencer un second cycle d'attente d'une duree (Ta) propre au module so respectif apres la detection d'une indication de fin d'emission (EOP) ou bien apres la fin du premier cycle d'attente (EOPTO); et des moyens (53, 89) pour valider une emission en reponse a I'indication de fin du second cycle d'attente (EOAD) si aucun preambule de porteuse ou signal de donnees n'a ete regu pendant ce temps-la. 12. Procede d'emission de signaux de donnees dans un systeme comprenant une pluralite de modules 55 incluant des stations et des dispositifs affectes aux stations, systeme dans lequel tout module accede a un milieu de transmission commun seulement sous la dependance d'une fonction de detection de porteuse pour emettre les donnees sous la forme de paquets, caracterise en ce que: — chaque module, quand son recepteur detecte une emission de signal, introduit un etat de non-emission et commence un cycle d'attente d'une duree (To) au moins egale au temps d'emission du 60 paquet le plus long (Tpmax), et en ce que — lors de la detection d'un delimiteur de fin d'emission (EOP) ou bien a la fin du cycle d'attente (EOPTO), chaque module pendant une sequence de tranches de temps commence toute emission de donnees seulement dans une tranche de temps qui lui est affectee s'il n'a pas detecte d'emission de signal pendant ce temps-la. 55 13. Procede d'emission de donnees par signaux infrarouges dans un systeme comprenant une

16 EP 0196 347 B1

pluralite de modules incluant des stations et des dispositifs assignes aux stations, systeme dans lequel tout module accede au canal d'emission infrarouge commun seulement sous la dependance d'une fonction de detection de porteuse pour emettre les donnees sous la forme de paquets, caracterise en ce que differentes — des emetteurs et recepteurs (31 , 33, 35) de tous les modules sont actives avec puissances 5 d'emission et sensibilites de reception selon le domaine de distance requis a couvrir, chaque module, quand son recepteur detecte une emission de signal infrarouge, introduit un etat de non-emission et commence un cycle d'attente d'une duree (To) au moins egale au temps d'emission du paquet le plus long possible (Tpmax), et en ce que — lors de la detection d'un delimiteur de fin d'emission (EOP) ou bien a la fin du cycle d'attente 10 (EOPTO), chaque module pendant une sequence de tranches de temps commence toute emission de donnees seulement dans une tranche de temps qui lui est affectee, s'il n'a pas detecte d'emission de signal infrarouge pendant ce temps-la. 14. Procede selon la revendication 13, caracterise en ce qu'un emetteur de tout module obtenant I'acces au canal infrarouge emet d'abord un preambule d'impulsions rectangulaires representant la 15 porteuse du signal infrarouge avant d'emettre un paquet de donnees. 15. Procede selon la revendication 14, caracterise en ce que le preambule est emis avec une puissance de signal superieure par rapport aux donnees ulterieures. 16. Procede selon la revendication 13, caracterise en ce que les paquets de donnees sont emis sous la forme de trames et en ce que chaque trame comprend un champ de commande comprenant des bits de 20 mode pour activer de fagon selective les modules. 17. Procede selon la revendication 13, caracterise en ce qu'a la suite de la detection d'un delimiteur de fin d'emission (EOP) ou a la suite de I'indication de la fin du cycle d'attente (EOPTO), chaque module les commence un second cycle d'attente representant un temps de garde (Tg) pour permettre a tous d'attente recepteurs de s'etablir a I'equilibre, et en ce qu'a la suite d'une indication de fin du second cycle 25 (EOG), un troisieme cycle d'attente est commence avec une duree (Ta) qui est selectionnee individuellement dans I'unite respective, et en ce que I'etat de non-emission est laisse pour le module respectif a la suite de I'apparition d'une indication de la fin (EOAD) du troisieme cycle d'attente. 18. Procede selon la revendication 13, caracterise en ce que chacun des modules, quand il a emis un paquet de donnees d'une duree donnee (Tp), inhibe toute emission de donnees pendant une periode au 30 moins egale a la duree du paquet emis (Tp), reduisant ainsi le rapport cyclique de son emetteur a une fraction du temps d'emission total possible pour permettre le refroidissement des diodes emettrices de lumiere entre les emissions. 19. Systeme pour interconnecter des modules emettant et/ou recevant des donnees incluant une pluralite de stations (11) et de dispositifs d'entree/sortie E/S associes (13, 15) et au moins un module 35 repeteur (17), par signaux infrarouges, I'information etant emise sous la forme de trames de paquets comprenant au moins un champ d'adresses et un champ d'information de commande, caracterise en ce que des moyens sont prevus dans chaque module pour activer le module respectif pour accepter ou bit de commande pour reemettre une trame de paquet regue seulement si ce module est selectionne par un 40 de mode affecte dans la trame respective, le champ d'information de commande comprenant des bits de commande de mode pour selectionner chacun I'un des modules individuellement ou pour selectionner un groupe de modules ayant la meme fonction dans le systeme. 20. Systeme selon la revendication 19, caracterise en'ce que chaque module (11, 13, 15, 17) comprend au moins un emetteur-recepteur infrarouge (31, 33, 35), et en ce que chaque emetteur-recepteur appartient 45 a I'une d'un nombre limite de categories hierarchiques ayant chacune une puissance d'emission et une sensibilite de reception differente, selon le domaine de couverture de distance requis des emetteurs- recepteurs de la categorie respective.

50

55

60

65

17 EP 0196 347 B1

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EP 0196 347 B1

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INTERFERENCE

STRENGTH OF SIGNAL RECEIVED

DISTANCE FROM SENDER

D-BOUNDARY C-BOUNDARY H-BOUNDARY

FIG. 4 TRANSMISSION MODEL

EP 0196 347 B1

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1 (EOG) i RESET CS LATCH WAIT FOR END OF C(t)-0 GUARD TIME

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i i REPORT TRANSMISSION WAIT FOR 1ST OF FOLLOWING EVENTS BOP TO HIGHER LAYERS EOAD

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REC'D CARRIER h-47 LOGIC CIRCUITRY FOR DATA DETECT ACCESS PROTOCOL s HANDLING CS MDE M5 -53 LATCH

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