| Pin | Name | Dir | Description |
|---|
| 1 | | | +5V 3-T regulator voltage supply (about +8V) |
| 2 | - | Dito |
| 3 | GND | - | Ground |
| 4 | READYA | - | System ready (10K pull-up to +5V) |
| 5 | GND | - | Ground |
| 6 | RESET* | OUT | System reset (active low) |
| 7 | GND | - | Ground |
| 8 | SCLK | nc | System clock (not connected) |
| 9 | LCP* | nc | CPU indicator 1=TI99 0=2nd generation (not connected) |
| 10 | AUDIO | IN | Input audio (=AUDIOIN) |
| 11 | RDBENA* | IN | Active low: enable flex cable data bus drivers (1K pull-up) |
| 12 | PCBEN | H | PCB enable for burn-in (always High) |
| 13 | HOLD* | H | Active low CPU hold request (always High) |
| 14 | IAQHA | nc | IAQ [or] HOLDA (logical or) |
| 15 | SENILA* | H | Interrupt level A sense enable (always High) |
| 16 | SENILB* | H | Interrupt level B sense enable (always High) |
| 17 | INTA* | IN | Active low interrupt level A (=EXTINT*) |
| 18 | LOAD* | nc | Unmaskable interrupt (not connected) |
| 19 | D7 | IN/OUT | Data bus, bit 7 (least significant) |
| 20 | GND | - | Ground |
| 21 | D5 | IN/OUT | |
| 22 | D6 | IN/OUT | |
| 23 | D3 | IN/OUT | |
| 24 | D4 | IN/OUT | |
| 25 | D1 | IN/OUT | |
| 26 | D2 | IN/OUT | |
| 27 | GND | - | Ground |
| 28 | D0 | IN/OUT | Data bus, bit 0 (most significant) |
| 29 | A14 | OUT | |
| 30 | A15 | OUT | Address bus, lsb. Also CRU output bit. |
| 31 | A12 | OUT | |
| 32 | A13 | OUT | |
| 33 | A10 | OUT | |
| 34 | A11 | OUT | |
| 35 | A8 | OUT | |
| 36 | A9 | OUT | |
| 37 | A6 | OUT | |
| 38 | A7 | OUT | |
| 39 | A4 | OUT | |
| 40 | A5 | OUT | |
| 41 | A2 | OUT | |
| 42 | A3 | OUT | |
| 43 | A0 | OUT | Address but, bit 0 (most significant) |
| 44 | A1 | OUT | |
| 45 | AMB | H | Extra address bit. Always High. |
| 46 | AMA | H | Extra address bit. Always High. |
| 47 | GND | - | Ground |
| 48 | AMC | H | Extra address bit. Always High. |
| 49 | GND | - | Ground |
| 50 | CLKOUT* | OUT | Inversion of phase 3 clock (=PHI3*) |
| 51 | CRUCLK* | OUT | Inversion of TMS9900 CRUCLOCK pin |
| 52 | DBIN | OUT | Active high = read memory |
| 53 | GND | - | Ground |
| 54 | WE* | OUT | Write Enable (derived from TMS9900 WE* pin) |
| 55 | CRUIN | IN | CRU input bit to TMS9900 |
| 56 | MEMEN* | OUT | Memory access enable (active low) |
| 57 | | | -12 Volts 3-T regulator supply voltage (about -16V) |
| 58 | | | Dito |
| 59 | | | +12 Volts 3-T regulator supply voltage (about +16V) |
| 60 | | | Dito |