32-WAY PORT FOR SINCLAIRS
EPROM SERVICES produces a 32-way port for the ZX-81 or Spectrum which has LEDs to indicate the state of its outputs. The device is based on an 8255 chip which is I/O-mapped to give 24 lines. One of the outputs is then fed to a set of eight flip-flops which produce the other eight lines.
A flip-flop gives two outputs which are always the opposite of each other, so if one is 0 the other is 1. Thai allows you to drive more devices but does not give more than 24 controllable two-state lines.
One of the facilities provided is for using the port to select other devices.
The PCB has no edge connector, so it has to be used with a motherboard or back-to-back connector.
Eprom Services is at 3 Wedgewood Drive, Roundhay, Leeds LS8 1EF. It charges £15 for the port and £24 for a motherboard for the Spectrum.