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TI-99/4A Side Port

  2                             44
+----------------------------------+
| ================================ |
+----------------------------------+
  1                             43

Pin Name Dir Description
1 VCC --> +5 Volts power supply
2 SBE --> Low if addr in >9000-94xx (sound port)
3 RESET* --> System reset (active low)
4 EXTINT* <-- External interrupt (active low)
5 A5 --> Address bus, bit 5
6 A10 --> Address bus, bit 10
7 A4 --> Address bus, bit 4
8 A11 --> Address bus, bit 11
9 DBIN --> Active high = read memory
10 A3 --> Address bus, bit 3
11 A12 --> Address bus, bit 12
12 READY <-- Active high = memory is ready
13 LOAD* <-- Unmaskable interrupt (=> BLWP @>FFFC)
14 A8 --> Address bus, bit 8
15 A13 --> Address bus, bit 13
16 A14 --> Address bus, bit 14
17 A7 --> Address bus, bit 7
18 A9 --> Address bus, bit 9
19 A15 --> Address bus, lsb. Also CRU output bit.
20 A2 --> Address bus, bit 2
21 GND --- Ground
22 CRUCLK* --> Inversion of TMS9900 CRUCLOCK pin
23 GND --- Ground
24 PHI3* --> Inversion of phase 3 clock
25 GND --- Ground
26 WE* --> Write Enable (derived from TMS9900 WE* pin)
27 GND --- Ground
28 MBE* --> Active low if addr in >4000-5FFF (card ROMs)
29 A6 --> Address bus, bit 6
30 A1 --> Address bus, bit 1
31 A0 --> Address bus, bit 0 (most significant)
32 MEMEN* --> Memory access enable (active low)
33 CRUIN <-- CRU input bit to TMS9900
34 D7 <-> Data bus, bit 7 (least significant)
35 D4 <-> Data bus, bit 4
36 D6 <-> Data bus, bit 6
37 D0 <-> Data bus, bit 0 (most significant)
38 D5 <-> Data bus, bit 5
39 D2 <-> Data bus, bit 2
40 D1 <-> Data bus, bit 1
41 IAQ <-- Interrupt acknowledged by TMS9900
42 D3 <-> Data bus, bit 3
43 VDD --> -5 Volts power supply
44 AUDIOIN <-- To sound generator AUDIO IN pin

Note: Direction is computer relative device.

Note: * = active low.

Caution: Bit 0 being MSB is strange.

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