Christmas 1979, Issue 5

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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 fault.

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:

  4. It follows the colours of the ribbon cables, but it doesn’t say so.
  5. R43 is missing from the drawing in the base of TR3
  6. My cassette interface would not work unless the variable resistor was adjusted such that the wiper gave 0 volts.
  7. 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 control.

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