ZX Spectrum 128 edge connector
The ZX Spectrum 128 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.
The ZX Spectrum +2
Notes on Connections
On the UK 128 the ULA clock pin is connected directly to the edge connector and is inverted by TR3 to drive the Z80.
On the +2 the ULA clock pin is inverted by a NOT gate to generate the clock for the Z80. It is then inverted again by a second NOT gate to generate the edge connector CK.
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.
Removed Video Outputs
Unlike the ZX Spectrum 16K/48K the ZX Spectrum 128 ULA generates RGB and Bright video signals rather than intensity and colour difference signals. The Y, U, and V signals are therefore not available so the pins previously used for them are left unconnected. Additionally the composite video signal has been removed.