ZX Spectrum 16K/48K edge connector

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Revision as of 23:01, 20 February 2012 by Guesser (talk | contribs) (us blank cell rather than "NC")
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Lower Upper
A14 1 1 A15
A12 2 2 A13
+5v 3 3 D7
+9v 4 4
0v 6 6 D0
0v 7 7 D1
!CK 8 8 D2
A0 9 9 D6
A1 10 10 D5
A2 11 11 D3
A3 12 12 D4
0v 14 14 !NMI
!Y 16 16 !MREQ
V 17 17 !IORQ
U 18 18 !RD
!BUSRQ 19 19 !WR
!RESET 20 20 -5v
A7 21 21 !WAIT
A6 22 22 +12v
A5 23 23 12v AC
A4 24 24 !M1
BUSACK 26 26 A8
A9 27 27 A10
A11 28 28

The ZX Spectrum 16k/48k expansion connector is a double sided card edge connector with a 0.1 inch spacing. The two rows of conductors are numbered from right to left looking into the rear of the computer. One pair of conductors are missing as there is an indexing slot cut out of the circuit board.

Notes on Connections

CPU Clock

The !CK signal, sometimes referred to as PHICPU is available on Lower Pin 8. This clock signal is generated by the ULA and is interrupted during contended memory access. This clock signal is inverted by a transistor switch to provide a clean clock edge for the Z80.

Key Slot

The key slot ensures correct alignment of a peripheral with the edge connector. This slot is the width of one conductor and lies between Pin 4 and Pin 6, i.e. Pin 5 does not exist.


  • Lower Pin 4 is connected to the +9 volt (nominal) DC supply from the ZX Spectrum PSU.
  • Lower Pin 3 is connected to the smoothed +5 volt DC output of the internal 7805 regulator.
  • Upper Pin 20 is connected to the -5 volt DC output of the internal power supply circuitry.
  • Upper Pin 22 is connected to the +12 volt DC output of the internal power supply circuitry.
  • Upper Pin 23 is connected to the oscillating voltage within the internal power supply circuitry. This is nominally 12 volts AC.
  • Lower Pins 6, 7, and 14 are connected to the 0 volt rail.

Video Outputs

Pin 15 on the lower side of the edge connector provides the same composite video signal that is fed into the UHF modulator. Lower pin 16 on the carries an inverted luminosity signal to use with the 'U' and 'V' colour difference signals provided on lower pins 18 and 17 respectively