After much checking with a cheap multimeter, I discovered that the
RESET line was low, ie: active. Tracing it back, it appeared that IC12a
was misbehaving. In fact it was a dud. A replacement chip cleared the
From here on everthing went smoothly. The memory board was
built and connected to the buss. Everything else worked first time.
Other Points of Interest
1) The graphics chip which the documentation says should be there
seems to be an optional extra.
2) The Basic chip needs a wait state to run properly, Nascom don’t
say anything about that in their advertising. So what the ads mean is
that although the Nascom 2 runs at 4 MHz, the Basic doesn’t. (With the
wait state, the BASIC averages 1.8 times the speed at 2 MHz without the
wait state, Ed.)
3) The numbering of PL/2/3/4 appears to be as follows, and not what
you would expect:
It follows the colours of the ribbon cables, but it doesn’t say so.
4) R43 is missing from the drawing in the base of TR3
5) My cassette interface would not work unless the variable resistor
was adjusted such that the wiper gave 0 volts.
6) The Veroboard tends to buckle in the middle when the edge
connectors are being soldered.
Now for a quick mod.
For those of you with Nascom 2 who want to run programs from
Nascom 1, the NASBUG monitors may be fitted on the extension memory
card in location 0 (& 1 for 2K monitors). Connect pin 16 of LSK1 to P5
on the memory card instead of pin 1 on LSK1. To give quick conversion,
use a single pole double throw switch as follows:
To switch without ruining anything in memory, execute a ‘HALT’
instruction before changing monitors, and use ‘RESET’ to recover