A simple GPIO board for a Sinclair ZX Spectrum computer with 16 digital inputs and 16 digital outputsDesigned by Tynemouth Software in United Kingdom
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What is it? This is a simple GPIO card you can plug into a Sinclair ZX Spectrum computer. It will provide 16 digital input lines and 16 digital output lines. Why did you make it? To get some simple...Read More…
This is a simple GPIO card you can plug into a Sinclair ZX Spectrum computer. It will provide 16 digital input lines and 16 digital output lines.
To get some simple digital IO from a Spectrum.
This is quite a simple simple board that can be used as the basis of some interesting projects
This is available as a bare PCB, as a full kit, or as a fully assembled and tested unit.
The input and output is controlled from two 8 bit ports, at addresses 0x01 and 0x03. They can be controlled via BASIC or assembler. In BASIC, the output command is
OUT 1, 255
This will turn all of the pins of output port 1 on (5v).
OUT 3, 0
This will turn all the pins of output port 2 off (0v).
The output is latched, and will retain this setting until it is changed.
The input command is
So for example,
PRINT IN 1
will print the value read from input port 1
IF IN 3 = 8 THEN GOTO 100
Will test to see if digital input port 2 has all input low bar pin 4
There are four 0.1" 10 pin headers. Each has 0V, D0-D7 and 5V on them, with 0V at the Spectrum end.
The output ports are 74HCT outputs, so can source or sink 6mA, which should be enough to drive an LED. If you want to drive a motor or relay, then a transistor buffer or driver chip should be used. The input ports are 74HCT inputs, so will recognise TTL level inputs. These should not exceed 5V. Pull up or pull down resistor will be required if connecting switches or other passive inputs. Unused input should be connected to ground or pulled up to the 5V rail.
Some good example projects for a simple IO board like this can be found in the Usborne range of computer books from the 1980s. PDF versions are available free from the publishers website. Usborne Books
This is a simple IO board, with no input or output protection, designed to be the basis of a larger project. This listing is the PCB, PCB+kit or built IO board only. It does not include the ZX Spectrum used in the photos, the test broadboard and cables, the Usborne book or my desk. The first versions of the PCB required a slight modification to fix the address decoding. This has been fixed in the current batch of boards, so not modifications are necessary.
This is designed for unmodified 48K ZX Spectrum and Spectrum+ machines. You may be able to get it to work on later 128K +2/+3 machines but this is unsupported as some adjustment to the port numbers may be necessary to avoid port numbers assigned to the internal hardware on these machines, there do not appear to be any available gaps in their address range.
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