IBM Printer Adapter
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----- ---- --_.------------ - - --- Technical Reference Options and Adapters Volume 2 IBM Industrial Computer IBM Monochrome Display and Printer Adapter Contents Monochrome Display Adapter Function . .. 1 Printer Adapter Function ........................................ 8 Logic Diagrams .............................................. 13 IBM Monochrome Display and Printer Adapter Monochrome Display Adapter Function The IBM Monochrome Display and Printer Adapter has two functions. The first is to provide an interface to the IBM Monochrome Display. The second is to provide a parallel interface for the IBM Printers. We will discuss this adapter by function. The IBM Monochrome Display and Printer Adapter is designed around the Motorola 6845 CRT Controller module. There are 4K bytes of RAM on the adapter that are used for the display buffer. This buffer has two ports to which the system-unit microprocessor has direct access. No parity is provided on the display buffer. Two bytes are fetched from the display buffer in 553 ns, providing a data rate of 1.8M-bytes/second. The adapter supports 256 different character codes. An 8K-byte character generator contains the fonts for the character codes. The characters, values, and screen characteristics are given in "Of Characters, Keystrokes, and Colors" in your Technical Reference system manual. IBM Monochrome Display and Printer Adapter Monochrome Display Adapter Function (continued) The following is a block diagram of the monochrome display adapter portion of the IBM Monochrome Display and Printer Adapter. Processo r (12) Memory address address (1g. multiplexer (10) (10) 2K memory 2K memory character attribute code Data (8) Processo r bus (8) data gating Character clock BDo-71 (8) Octal Octal MA 1 latch latch RA Character Attribute AO (4) generator decode MC6845 Chip CRTC select DOr LK Shift Timing register signals Video process Serial dots logic HSYNC VSYNC CURSOR DISPEN Character r clock J l Monitor direct drive outputs IBM monochrome display adapter block diagram IBM Monochrome Display and Printer Adapter 3 Monochrome Display Adapter Function (continued) 7 6 5 4 3 2 0 Character code even address (M) 7 6 5 4 3 2 0 BL R G B R G B Attribute code odd address (M + 1) I I I Foreground Intensity Background Blink The adapter decodes the character attribute byte as defined above. The blink and intensity bits may be combined with the foreground and background bits to further enhance the character attribute functions listed below: Background Foreground R G B R G B Function 0 0 0 0 0 0 Non-display 0 0 0 0 0 1 Underline 0 0 0 1 1 1 White character/black background 1 1 1 0 0 0 Reverse video The 4K display buffer supports one screen of the 25 rows of 80 characters, plus a character attribute for each display character. The starting address of the buffer is hex BOOOO. The display buffer can be read using direct memory access (DMA); however, at least one wait state will be inserted by the system-unit microprocessor. The duration of the wait state will vary, because the microprocessor/monitor access is synchronized with the character clock on this adapter. Interrupt level 7 is used on the parallel interface. Interrupts can be enabled or disabled through the printer control port. The interrupt is a high-level active signal. IBM Monochrome Display and Printer Adapter 5 Monochrome Display Adapter Function (continued) Bit number Function 0 + Horizontal drive 1 Reserved 2 Reserved 3 + Black/white video 6845 CRT status port (Hex 3BA) Connector Specifications 9-Pin Monochrome Display connector At standard TTL levels Ground 1 Ground 2 Not used 3 Not used 4 IBM IBM Not used 5 Monochrome Monochrome + Intensity 6 Display Display + Video 7 and Printer + Horizontal 8 Adapter - Vertical 9 Note: Signal voltages are 0.0 to 0.6 Vdc at down level and +2.4 to 3.5 Vdc at high level. Connector specifications IBM Monochrome Display and Printer Adapter 7 Printer Adapter Function (continued) The following is a block diagram of the printer adapter portion of the Monochrome Display and Printer Adapter. 8 25-pin D-shell I E connector ~us buffe ...r8.......... ~Data latch........... _8---1~ r-+" Enable ,.. Clock .J!... Trans ceiver r DIR DIR O.C. "'R'8ad drivers SLCTIN AEN -+- data STROBE Write data Command I---------+~ AUTO decoder Write control FD XT Read status Read INIT control ~ Bus Control buffers latch • Enable! ~ Clock ~ 5 ERROR -. Enable SLCT ~ Clear PE ACK Reset ~----------------~------------~ BUSY Printer adapter block diagram IBM Monochrome Display and Printer Adapter 9 Printer Adapter Function (continued) IBM monochrome display and printer adapter Input from address hex 3BC This instruction presents the system-unit microprocessor with data present on the pins associated with the output to hex 3BC. This should normally reflect the exact value that was last written to hex 3BC. If an external device should be driving data on these pins at the time of an input (in violation of usage ground rules), this data will be ORed with the latch contents. IBM monochrome display and printer adapter Input from address hex 3BD This instruction presents the realtime status to the system-unit microprocessor from the pins as follows. Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Pin 11 Pin 10 Pin 12 Pin 13 Pin 15 - - - IBM monoch rome display and printer adapter Input from address hex 3BE This instruction causes the data present on pins 1, 14, 16, 17, and the IRQ bit to be read by the system-unit microprocessor. In the absence of external drive applied to these pins, data read by the system-unit microprocessor will match data last written to hex 3BE in the same bit positions. Notice that data bits 0-2 are not included. If external drivers are dotted to these pins, that data will be ORed with data applied to the pins by the hex 3BE latch. Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 -- -- -- IRQ Pin 17 Pin 16 Pin 14 Pin 1 Enable Por = 0 Por = 1 Por = 0 Por = 1 Por = 1 These pins assume the states shown after a reset from the system-unit microprocessor. 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