PCjr video gate array pinout
DIP-40. PCjr video: modes, palette and the video memory interface.
The PCjr video gate array takes the CPU video writes and makes the CRT timing and color. It does the job of the CGA card, built into the planar: with the 6845 (ZM21) it shares the system RAM between the CPU and the display, and it drives the RGBI, composite color and TV sync outputs. IBM part 1503730, 40 pins, at ZM36. Pin names are as drawn in the Technical Reference; IBM publishes no data sheet for it.
Open the interactive GA pinoutPins
| Pin | Name | Type | Signal |
|---|---|---|---|
| 1 | VCC | power | +5 V. |
| 2 | CLK | clock | 14 MHz clock. |
| 3 | /MEM CS | ctrl | Video RAM select (-VIDEO RAM CS from the 24S10 decoder ZM56). |
| 4 | MEM CYC | ctrl | Memory cycle, from a 74LS00 gate (ZM58) on -XMEMW and -XMEMR. |
| 5 | /IO CS | ctrl | Gate array I/O select (-GA I/O CS). |
| 6 | /IOW | ctrl | I/O write (-ZIOW). |
| 7 | /IOR | ctrl | I/O read (-ZIOR). |
| 8 | CURSOR | video | Cursor, from the 6845. |
| 9 | D2 | data | Data bit 2 (ZD2). |
| 10 | D1 | data | Data bit 1 (ZD1). |
| 11 | D0 | data | Data bit 0 (ZD0). |
| 12 | D3 | data | Data bit 3 (ZD3). |
| 13 | D4 | data | Data bit 4 (ZD4). |
| 14 | CCG | video | CCG control output (to the board logic; name as drawn). |
| 15 | ACG | video | ACG control output (to the board logic; name as drawn). |
| 16 | GATE | ctrl | GATE strobe to the video latches. |
| 17 | GND | ground | Ground. |
| 18 | RAS | ctrl | RAM row strobe timing. |
| 19 | I | video | Intensity output. |
| 20 | R | video | Red output. |
| 21 | G | video | Green output. |
| 22 | B | video | Blue output. |
| 23 | CCLK | video | Character clock to the 6845. |
| 24 | GND | ground | Ground. |
| 25 | CRT/CPU | ctrl | Selects whether the CRT or the CPU owns the video RAM address lines. UNVERIFIED |
| 26 | COMP COLOR | video | Composite color output. |
| 27 | TV HOR | video | Horizontal drive. |
| 28 | TV VERT | video | Vertical drive. |
| 29 | VRDY | ctrl | Video ready: holds the CPU while the video RAM is busy. UNVERIFIED |
| 30 | DE | video | Display enable, from the 6845. |
| 31 | VERT IN | video | VSYNC from the 6845. |
| 32 | HOR IN | video | HSYNC from the 6845. |
| 33 | MD7 | data | Video memory data bit 7, read in. On the board the 4164 DOUT pins (sheet 4) and the character latch ZM70 (sheet 5) drive this bus; writes go to the RAM DIN pins by another path. UNVERIFIED |
| 34 | MD6 | data | Video memory data bit 6, read in. On the board the 4164 DOUT pins (sheet 4) and the character latch ZM70 (sheet 5) drive this bus; writes go to the RAM DIN pins by another path. UNVERIFIED |
| 35 | MD5 | data | Video memory data bit 5, read in. On the board the 4164 DOUT pins (sheet 4) and the character latch ZM70 (sheet 5) drive this bus; writes go to the RAM DIN pins by another path. UNVERIFIED |
| 36 | MD4 | data | Video memory data bit 4, read in. On the board the 4164 DOUT pins (sheet 4) and the character latch ZM70 (sheet 5) drive this bus; writes go to the RAM DIN pins by another path. UNVERIFIED |
| 37 | MD3 | data | Video memory data bit 3, read in. On the board the 4164 DOUT pins (sheet 4) and the character latch ZM70 (sheet 5) drive this bus; writes go to the RAM DIN pins by another path. UNVERIFIED |
| 38 | MD2 | data | Video memory data bit 2, read in. On the board the 4164 DOUT pins (sheet 4) and the character latch ZM70 (sheet 5) drive this bus; writes go to the RAM DIN pins by another path. UNVERIFIED |
| 39 | MD1 | data | Video memory data bit 1, read in. On the board the 4164 DOUT pins (sheet 4) and the character latch ZM70 (sheet 5) drive this bus; writes go to the RAM DIN pins by another path. UNVERIFIED |
| 40 | MD0 | data | Video memory data bit 0, read in. On the board the 4164 DOUT pins (sheet 4) and the character latch ZM70 (sheet 5) drive this bus; writes go to the RAM DIN pins by another path. UNVERIFIED |
Fitted in
- IBM PCjr 4860 ZM36 (PCjr Technical Reference, sheet 4 of 17, and the layout on sheet 17); IBM 1503730 on the photographed board
Sources
- PCjr Technical Reference (Nov 1983), Video Subsystem (gate array uses IRQ5 for vertical retrace), p. 2-82
- PCjr Technical Reference (Nov 1983), System Board sheet 4 of 17, p. B-6: GATE ARRAY ZM36, all 40 pins
- PCjr Technical Reference (Nov 1983), System Board sheet 17 of 17, p. B-19: component layout (ZM36)