TI-99/4A Side Port

Available on TI-99/4A computers. On the right side

Pinout

   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.

Contributions

Joakim Ögren