INTRODUCTION TO CONTROL APPLICATIONS
THE NEW I/O port from Multitron gives the Spectrum a means of communicating with the outside world. Using the port it could control motors, turn lights on and off or detect when a switch has been closed. It transfers signals to and from the outside in a form the CPU can understand.
For the technically-minded it is an uncased PCB with through connector based on the Intel 8255 AP-5 chip. The chip has three 8-bit ports - A, B and C - and a control register (D), the addresses being 31, 63, 95 and 127 respectively. Each port can be set to either input or output with the upper and lower nibbles of port C capable of being set independently to either. Two more modes of operation are available, which allow strobed 110 with handshaking and strobed bidirectional operation; in both cases the data can be latched. Details are given in the user manual supplied.
Connections to the board are either by a 28-way Spectrum-style edge connector or soldercon pins - breadboard style. The manual gives comprehensive details of how the port works and how to set it up. It also includes two brief programs, one to make the port test itself and one to show binary numbers being output to LEDs.
One thing it does not do is to give simple circuit diagrams to show how to connect a LED or perhaps a relay.
At a very reasonable £13.50 plus 35 pence p&p, including manual, it provides a cheap introduction to control applications.
The board is available from Multitron, 5 Milton Close, Headless Cross, Redditch, Worcs. B97 5BQ. Tel: 0527 44785.