ZX Spectrum pinouts

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Contents

ZX Bus

The original Sinclair ZX Spectrum Expansion Bus comes in several variants for different computers.

ZX bus expansion pinout

component side = A

solder side = B

ZX bus expansion pinout

The common ZX bus expansion pinout follows:

pin A B
1 A15 A14
2 A13 A12
3 D7 +5V
4  ?  ?
5 X X
6 D0 GND
7 D1 GND
8 D2 CLK
9 D6 A0
10 D5 A1
11 D3 A2
12 D4 A3
13 /INT  ?
14 /NMI GND
15 /HALT  ?
16 /MREQ  ?
17 /IORQ  ?
18 /RD  ?
19 /WR /BUSRQ
20 -5V /RESET
21 /WAIT A7
22 +12V A6
23 -12V A5
24 /M1 A4
25 /RFSH /ROMCS
26 A8 /BUSACK
27 A10 A9
28  ? A11

ZX bus expansion pinout differences

Different ZX Spectrum variants had slightly different bus expansion pinouts:

pin 48K/+ 128K/+2 2A, 2B and 3
4A NC NC ROM1 OE
20A -5V -5V NC
23A +12V +12V -12V
28A NC NC RESET
4B 9V 9V NC
13B IORQGE IORQGE NC
15B VIDEO NC ROM2 /OE
16B Y NC DISK /RD
17B V NC DISK /WR
18B U NC MOTOR ON
25B ROMCS ROMCS NC

Didaktik variation

The Didaktik, the clone from the Czechoslovakia, had these differences:

pin Dida
20A /ROMCS-D
22A NC
23A NC
26B /BUSAK

AY sound chip

The AY-3-8910 is a 3-voice programmable sound generator (PSG) designed by General Instrument, also produced under license by Yamaha, later also under the Microchip Technology brand.

The same silicon chip was sold in three different packages: AY-3-8910, AY-3-8912, AY-3-8913.

AY-3-8910 pinout

The AY-3-8910 is a 40-pin package, it contains two general-purpose 8-bit parallel I/O ports A and B.

AY-3-8910 chip pinout

AY-3-8912 pinout

The AY-3-8912 is a 28-pin package, it contains one general-purpose 8-bit parallel I/O port A, while the other parallel port is simply not connected to any pins.

The 8912 was the most widely used variant.

AY-3-8912 chip pinout

AY-3-8913 pinout

The AY-3-8913 is a 24-pin package, with both parallel ports not connected.

AY-3-8913 chip pinout

decoding

register read: FFFD

data write: BFFD

data read: FFFD

tested address lines: A1, A14, A15

tested control signals: /WR, /RD, /IORQ

Disclaimer

Warning: This collection is no more complete than informative!

Petr Sladek, the author of this ZX Spectrum pinouts collection,

reserves no warranty or

for informative purposes only,

do not build, modify nor enhance your devices

based on information found on this site,

you may seriously harm yourselves, your close ones,

your chips or your pets.

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