Pinout diagram
Used in Retro Machine Hubs
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Summary specifications
Full pin reference
| Pin | Name | Group | Direction | Levels | Description |
|---|---|---|---|---|---|
| 1 | VSS1 | Ground | Power | 0 V | Primary digital ground. |
| 2 | A3 | Address Bus | Input | TTL | Address bit 3 (selects GTIA registers at $D000-$D01F). |
| 3 | A4 | Address Bus | Input | TTL | Address bit 4. |
| 4 | R/W | Control | Input | TTL | Read/Write input. |
| 5 | /CS | Control | Input | TTL, active low | Chip Select input ($D000-$D0FF). |
| 6 | D7 | Data Bus | Bidirectional | TTL | Data bus bit 7. |
| 7 | D6 | Data Bus | Bidirectional | TTL | Data bus bit 6. |
| 8 | T0 (TRIG0) | I/O | Input | TTL (active low) | Joystick 1 Fire Button input ($D010). |
| 9 | T1 (TRIG1) | I/O | Input | TTL (active low) | Joystick 2 Fire Button input ($D011). |
| 10 | T2 (TRIG2) | I/O | Input | TTL (active low) | Joystick 3 Fire Button input ($D012; unused on 2-port XL/XE). |
| 11 | T3 (TRIG3) | I/O | Input | TTL | Joystick 4 Fire Button (on 400/800) OR Cartridge Present sense (`RD5`) on XL/XE! |
| 12 | S0 (START) | I/O | Bidirectional | TTL (active low) | START console button input ($D01F CONSOL bit 0). |
| 13 | S1 (SELECT) | I/O | Bidirectional | TTL (active low) | SELECT console button input ($D01F CONSOL bit 1). |
| 14 | S2 (OPTION) | I/O | Bidirectional | TTL (active low) | OPTION console button input ($D01F CONSOL bit 2 — hold at power-on to disable BASIC!). |
| 15 | S3 (SPKR) | I/O | Output | TTL | Console key-click speaker / audio mix output ($D01F CONSOL bit 3). |
| 16 | DEL | Analog | Input | Bias voltage | Colour phase delay bias input (connected to COLOR pot R38 — adjusts hue spacing across the 15 colours!). |
| 17 | VCC | Power | Power | +5 V | +5 V main supply. |
| 18 | D4 | Data Bus | Bidirectional | TTL | Data bus bit 4. |
| 19 | D5 | Data Bus | Bidirectional | TTL | Data bus bit 5. |
| 20 | VSS2 | Ground | Power | 0 V | Video / delay-line ground. |
| 21 | COLOR | Analog | Output | Open-collector chroma | Chrominance phase output (tapped by UAV video mod and 800XL Pin 5 S-Video Chroma restore!). |
| 22 | LUM1 | Analog | Output | Open-collector | Digital Luminance DAC bit 1. |
| 23 | LUM2 | Analog | Output | Open-collector | Digital Luminance DAC bit 2. |
| 24 | LUM3 | Analog | Output | Open-collector | Digital Luminance DAC bit 3 (MSB). |
| 25 | LUM0 | Analog | Output | Open-collector | Digital Luminance DAC bit 0 (LSB — note Pin 25 is LUM0 while Pins 22-24 are LUM1-3!). |
| 26 | D3 | Data Bus | Bidirectional | TTL | Data bus bit 3. |
| 27 | D2 | Data Bus | Bidirectional | TTL | Data bus bit 2. |
| 28 | FPHI0 | Clock / Timing | Input | TTL 3.58 MHz | Fast Phase 0 master pixel clock (3.58 MHz NTSC / 3.55 MHz PAL). |
| 29 | CSYNC | Analog | Output | TTL sync | Composite Video Sync output. |
| 30 | PHI2 | Clock / Timing | Input | TTL 1.79 MHz | System Phase 2 CPU clock. |
| 31 | AN2 | I/O | Input | TTL | ANTIC pixel/command bus bit 2. |
| 32 | AN1 | I/O | Input | TTL | ANTIC pixel/command bus bit 1. |
| 33 | AN0 | I/O | Input | TTL | ANTIC pixel/command bus bit 0. |
| 34 | D1 | Data Bus | Bidirectional | TTL | Data bus bit 1. |
| 35 | D0 | Data Bus | Bidirectional | TTL | Data bus bit 0. |
| 36 | OSC | Clock / Timing | Input | Subcarrier | Colourburst oscillator reference (3.5795 MHz NTSC / 4.4336 MHz PAL). |
| 37 | /HALT | Control | Input | TTL, active low | ANTIC DMA Halt status input (tells GTIA when Player-Missile DMA bytes are on D0-D7). |
| 38 | A0 | Address Bus | Input | TTL | Address bit 0. |
| 39 | A1 | Address Bus | Input | TTL | Address bit 1. |
| 40 | A2 | Address Bus | Input | TTL | Address bit 2. |
Common uses and repair diagnostics
Designed by George McLeod to supersede the earlier 128-colour CTIA (CO10745, 100% pin-compatible!), the 40-pin Atari GTIA (Graphics Television Interface Adaptor) receives the 3-bit AN0-AN2 pixel stream from ANTIC, overlays four 8-bit Player sprites and four 2-bit Missile sprites with hardware collision detection, adds three 80-pixel-wide GTIA modes (16-shade monochrome Mode 9, 9-colour Mode 10, and 16-hue Mode 11 = 256 total colours!), outputs a 4-bit digital Luminance bus (LUM0-LUM3, Pins 22-25) plus phase-delayed Chrominance (COLOR, Pin 21) and Composite Sync (CSYNC, Pin 29), and reads the four joystick fire buttons (T0-T3) and the START, SELECT, and OPTION console keys (S0-S2)!
Used in all Atari 400, 800 (replacing early CTIA), 1200XL, 600XL, 800XL, 65XE, 130XE, XEGS, and Atari 5200 systems. Notice that installing an Ultimate Atari Video (UAV) board is a simple solderless plug-in on the 40-pin GTIA socket because LUM0-LUM3 (Pins 22-25), COLOR (Pin 21), and CSYNC (Pin 29) all originate right on the GTIA!
- If START, SELECT, or OPTION console keys do not work even after cleaning the keyboard Mylar, check Pins 12, 13, and 14 on the GTIA (they pull low to 0 V when pressed).
- If Joystick Fire buttons are stuck or ignored, check Pin 8 (T0) and Pin 9 (T1).
- Wrong ordrifted colours on screen: adjust the internal COLOR trimpot connected to Pin 16 (DEL).