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Expansion connector

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

Stuart Conner's Simple TMS9995 board build

KeithKeith 11/27/2022 at 19:060 Comments

Pinout

nc140A15/CRUOUT
nc239A14
CLKOUT338A13
D7437A12
D6536A11
D5635A10
D4734A9
D3833A8
D2932A7
VCC1031VSS
D11130A6
D01229A5
CRUIN1328A4
!INT4/EC1427A3
!INT11526A2
IAQ/HOLDA1625A1
!DBIN1724A0
!HOLD1823READY
!WE/!CRUCLK1922!RESET
!MEMEN2021!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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