Build the TVT-6: ' A Low-Cost '· '· ' ' ' '· '· '· DIRECT VIDEO PARTI DISPLAY $35 microcomputer ''add-on'' provides: • User-selectable line lengths • Scrolling • Up to 4k on-screen characters with only 3-MHz bandwidth BY DON LANCASTER The TVT-6 connected to a KIM-1. ADDRESS 02 CLOCK -+------------. hanks to some software tricks, a simple and low-cost add-on circuit, T BIT 7 TV OUTPUT and a new way to speed up a micro­ IJ2) processor, you can now build a video in­ terface for your microcomputer for an in­ BITS 11)- 6 vestment of only $20 to $35. The TVT-6 video system described here permits the choice of virtually any format including 16/32 (16 lines of 32 characters), 16/64, DECODE ENABLE or 32/64. It also features full editing ca­ CS SOURCE pability and full-performance cursor. Al5 Al4 In spite of its simplicity (10 low-cost Al3 IC's), the circuit employs a new ap­ Al2 proach to video processing that permits All up to 4000 characters to be displayed on-screen within a 3-MHz bandwidth. Al­ though the TVT-6 was designed for the A5 A4 .,_ -. 6502 microprocessor based KIM-1, soft­ R/W A3 - . ' --·- �- - ; ware can be used to easily map into the A2 �-; - JOLT, EBKA, or Ohio Scientific mi­ Al ·-: ��... ·- :.� crocomputers. In addition, the TVT-6 can be adapted to other microproces­ DATA BUS TVT-6 sors, including the popular 6800, 8080, KIM-I OR OTHER and ZSO, It is easiest to use with 16- MICROPROCESSOR SYSTEM address-line systems that operate on a Fig. 1. TVT-6 block diagram single 5-volt supply and 1-µs cycle time. and truth table for the PROM. JULY 1977 47 www.americanradiohistorv.com { I GND GND 2 GND { PIN 7 OF IC2-IC6,IC9, ICIO � �� PIN 8 OF ICI, ICS PIN 10 OF IC7 SPARES 5 NC I-MHz CLOCK 6 VCL-+-FIG4 @ 7 VD7------------� 8 VD6 NC 10 24 II 12 6 15 22 9 VD5--------------'---'=i � 21 4 9 � 6� 10 VD4 --------------;.--"'i FIG'4© �i�5�� 20 5 14 II VD3 -------------'---'=i IC7 ICS Rl3 ---- ----------'--'-'"I1 9 6 3 4.7 K 12 vD2-------------'---"'-t 2513 74165 +5\' 13 VDI 18 7 4 17 8 5 ::r:: 14 vD0---------------'--'-'-! cs 33pF 14 2 I LOAD FIG4 ® CLOCK � =TEST POINT FIG4 @) GND:GROUND D5 RV:RAW VIDEO (ENHANCED) IN4148 CV: COMPOSITE VIDEO VR: VERTICAL RATE HR: HORIZONTAL RATE DISPLAY MEMORY 15 CSI------'----. cs 1s cso------'---. R8 Fig. 2. Parallel outputs { :: ::� 4.7K ����� --------' from character generator AD •=40 11 (IC5) IC7 are converted into 20 Al3-----------'-------� * = 74LS08 (IC6) serial dcita in ICB. l ® +5V � �FIG3 Pa1·ts of IC5 and IC6 HR forn gating circuits. F I G3 © Other systems will require software and microprogramming translation for their particular machine languages. In this first of a two-part article, we will cover the hardware and construction de­ tails for the TVT-6. Next month, we will •= IC2, 74LSOO cover debugging, some useful software FIG4 for the system, and provide instructions J 21 Al4 LENGTH I on how to couple the TVT-6 to other mi­ I J 22 Al5 +5V 15 64 32 croprocessors. 14 ADDRESS 23 A5 13 LINES 24 A4 (0,6-10 12 ICI NOT USED) 25 A3 Circuit Operation. A block diagram II 5610 26 A2 of the TVT-6. as used with the KIM-1 10 27 Al system, is shown in Fig. 1. The complete schematic diagram of the video system 28 DB7 29 DBS is shown in Figs. 2 through 4. 30 DB5 As shown in Fig. 1. bits through 6 31 084 <I> DATA from the "upstream tap" on the KIM dis­ SUS 32 DB3 play memory drive character generator 33 D82 /C7 whose blanking and formatting are 34 DBI 35 DB0 helped along by the AND gates in /C6. £ +5V The cursor bit (bit 7) is stripped off the +5V,.2A 36 +5V--- �----� ----+-P I N 14 OF IC2-IC6,IC9,ICIO _L___ ...._ _L __ PIN 16 OF ICI, IC8 upstream tap and routed to cursor blink­ L �._ ;r PIN 24 OF IC7 Cll-;:r-I Cl2! Cl3i er /CS, which introduces a blinking cur­ .lµF .1 µ .1µF _ _... sor into the character generator's enable input. Fig. 3. New SCAN instruction uses PROM ICl, which The parallel outputs from /C7 go to also has the line length option in its circuit. 48 POPULAR ELECTRONICS www.americanradiohistorv.com +5V 8 R7 220fl R5 22K R6 22K 6 Rl8 2.2K CIO 240 pF �t--11 1 ....._,WAYW-- 1 IOOK :M Rl4 Rl7 2.2K �os'N *: IC9,74LS32 •=IC4,74LS04 cs cb lI: H ::::r:: FIG2 FIG3 FIG3 .047µF Fig. 4. Video combiner (IC10), offset generator (Ql) and sync deluy circuits deliver video to TV. Gated clock (IC4) controls parallel-to-serial converter. CI, C7--0.0l-µF Mylar capacitor PARTS LIST R11 -100 ohms C2-120-pF polystyrene capacitor R12-1 ilOO ohms C3. C 11. C 12. C13--0. l-µF Mylar capacitor R14.R 15-100,000-ohm pc-type (upright) po­ C4-l 50-pF polystyrene capacitor ICS-74165 PISO shift register tc'ntiometcr C5-2200-pF polystyrene or Mylar capacitor IC9-74LS32 quad OR gate IC Misc.-Sockets for !C's (seven 14-pin, two C&-33-pF polystyrene capacitor IC 10--4066 quad analog switch IC 16-pin. one 24-pin); 36-contact edge con­ C8--0.ll47-µF Mylar capacitor J 1. J2-Pc-mount phono jack (Molex No. nector with 0. 156" centers (Amphenol 2 25 C9-330-pF polystyrene capacitor 15-2 4-2181 or similar) or similar): solid hook-up wire for jumpers: CI 0--2.W-pF polystyrene capacitor Q 1-2N44()2 or MPS6523 (Motorola) transis­ insulated sleeving; test-point terminals (5); DI through D5-IN 4148 silicon diode tor solder: etc. ICl-IM5610 32x8 PROM (or similar) The' following resistors are \!.i wall, 10% toler- IC2-74LSOO quad tri-state NAND gate IC anc�: Note: The following items are available from IC3--4013 dual-D flip-flopIC RI, RI 0--470 ohms PAIA Electronics, Box 14359, Oklahoma IC4-74LS04 hex inverter IC R2-10.000 ohms City. OK 73114: No. PVI-1 PC printed cir­ IC5--401 I quad NAND gate IC R3.R7-220 ohms cuit board for $5.95; complete kit of all IC6-74LS08 quad AND gate IC R4.R 16,R 17,RIS-2200 ohms pans. No. PVl-1K, for $34.95 (specify IC7-25I 3 character generator (must be sin­ R5.R&-22,000 ohms hlank or KIM-I programmed /Cl); KIM-I gle-supply type. such as General Instru­ R8,R13.R 19---4700ohms coded casselle. with programs, No. PVI­ ments No. R0-3-2513) R9-2.2 megohms ICC, for $5.00. All prices postpaid. shift register /CB, where they are con­ The serial video from /CB goes to the The vertical and horizontal timing sig­ verted into a serial video signal. The TV Bandwidth Compensator in /C9, nals from JC2 in the gating circuit are de­ clock and load commands for /CB come which predistorts the video by delaying layed by /C3. The display positioning from gated oscillator /C4, which derives the video output and OR'ing it against it­ can be varied by potentiometers R14 its signals from the microcomputer's self. This widens the vertical portions of and R15. The vertical and horizontal clock. It is important that the correct all characters to generate clean and sync signals are combined with the en­ clock phase be selected to permit the crisp characters that require minimum hanced video from IC9 into video com­ loading of /CB to occur when the output bandwidth. The amount of widening is biner JC10. The output from JC10, avail­ of the character generator is valid and determined by C2 (Fig. 4). The optimum able at J1, is composite video, with the settled. This is phase 2 in the KIM-1. (If value of C2 is obtained when the gener­ sync tips at ground, black at 0.4 volt, and you are using a different µP based com­ ated M or W in the video display just white at 1.6 volts. This output can be puter, check this detail.) barely closes. used to drive conventional video moni- JULY 1977 49 www.americanradiohistorv.com tors and converted TV receivers. The video output from IC10 is also fed to 01, which is offset to deliver a +4-volt output for the white level. This output, available at J2, can be connected directly to the first video amplifier of most transformer­ powered solid-state TV receivers (see box for details) without requiring biasing, coupling, or translation circuits. Two options are provided with the TVT-6, both of which are jumper select­ ed The LENGTH option allows a choice of either 32 or 64 characters/line. The CURSOR option gives the choice of either no cursor or allows the cursor to be dis­ played under software control. Construction. The actual-size etch­ ing and drilling guide for the printed cir­ cuit board used in the TVT-6 is shown in Fig. 5, along with the component-instal­ lation diagram. Start assembly by install­ ing and soldering into place the 21 jump­ ers and test points. (Note that insulated sleeving must be used on two of the long junpers.) Install the IC sockets, resis­ tors, capacitors, diodes, jacks, and posi­ tion controls R14 and R15. Do not install the IC's at this time. The correct IC in­ stallation sequence and the waveforms to be observed will be discussed in Part 2 next month.