EPROM Services 32-way Port
Hardware: Add-on
Eprom Services · 1983 · Pound sterling 15.00
32-way I/O port based on the 8255 chip. It uses a standard 24 line port with one output fed into eight flip-flops to gain the extra lines. These extra lines are four pairs which can only be oposite each other. (if four are 0, then the other four must be 1). This port requires a motherboard for connection costing £24.00
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In the magazines 1
Sinclair User #13Apr 1983 · p.26
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 [redacted]. It charges £15 for the port and £24 for a motherboard for the Spectrum.
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