One of those “I really must get one” boards… It was really one for the
hardware hackers.

This unit came with one or two PIO ICs fitted (if I remember correctly).
The CTC (clock/timer/controller) could be added as an extra. Notice that
the necessary connectors and IC sockets were also optional extras!

Further optional extras were a third PIO and a UART (the latter giving a single serial I/O port). The UART could use a dedicated baud rate clock circuit or the CTC could be used to give variable bit rates where odd systems were used!

More than one of these boards could be fitted to a system and software selected. In the usual Nascom manner, all the I/O addresses used were link-selectable for maximum versatility and confusion. 🙂

Lucas Logic provided their usual inspiring documentation for this board…

…but at least they provided a circuit diagram (Warning – 700kB file). The board fully supported the interrupt structure of the Nasbus (but the UART wasn’t included in the interrupt system).

Nascom Pages