Expansion connector

A project log for Stuart Conner's Simple TMS9995 board build

Stuart Conner's Simple TMS9995 board build

Keith • 11/27/2022 at 19:06•0 Comments

Pinout

nc	1	40	A15/CRUOUT
nc	2	39	A14
CLKOUT	3	38	A13
D7	4	37	A12
D6	5	36	A11
D5	6	35	A10
D4	7	34	A9
D3	8	33	A8
D2	9	32	A7
VCC	10	31	VSS
D1	11	30	A6
D0	12	29	A5
CRUIN	13	28	A4
!INT4/EC	14	27	A3
!INT1	15	26	A2
IAQ/HOLDA	16	25	A1
!DBIN	17	24	A0
!HOLD	18	23	READY
!WE/!CRUCLK	19	22	!RESET
!MEMEN	20	21	!NMI

Pinout matches the TMS9995 CPU apart from pins 1 and 2 which are connected to the crystal on the CPU. If you wanted to drive the CPU from an external clock source, then you could wire pin 2 from the connector to the CPU.

Signals

A0...15 are like A15...0 of the Z80
!MEMEN is like !MREQ of the Z80
!WE    is like !WR of the Z80
!DBIN  is like !RD of the Z80
!HOLD  is like !BUSRQ of the Z80
HOLDA  is like !BUSAK of the Z80 (but inverted)
READY  is like !WAIT of the Z80

The signal names look strange at first but have conventional equivalents.

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