INMC 80 News

If you have any further comments or have had experience with the Gemini or Henelec system, please let us know at the Merseyside Group. (We’d like to know as well. Ed)

If you want to contact the Merseyside Nascom Users Group please do so through the group secretary:

Graham W. Myers,
_, _________ _____,
Wincham,
Northwich,
Cheshire.

Keyboard/​Disk Problem

Whilst on the subject of disks, our thanks to one intrepid gentleman who has fitted his CP/M disk system to a Nascom 1. Now it is well known that some Nascom ls will run quite happily at 4 MHz, and even if they don’t then a bit of RAM swopping and changing the Z80 will usually bring them into line. Even so, there have been recurring reports of unreliability for no apparent reason, and this has usually been put down to ‘a slow chip somewhere’. Well Mr. Hodgson has an N1, which until he fitted his disk system, would work perfectly at 2 MHz, and ‘so so’ at 4 MHz. Odd occasions when things became unreliable, but generally speaking, Ok. Well on went the disk system, and it worked perfectly at 2 MHz but not at all at 4 MHz.

Mr. Hodgson took up the challenge to see what was happening, his investigation led to a most intriguing solution. As Holmes is quoted as saying, “When you have eliminated the possible, then what ever is left no matter how impossible....” {or words to that effect). Mr. Hodgson was left with the keyboard !!!! The keyboard has a monostable which times the keyboard counter reset pulse. He found that the reset pulse was just a ‘nth’ too long and that it didn’t come off until just after the first counter pulse arrived. Reducing the value of the timing resistor not only put the keyboard counter straight, but cured all the other unreliability problems as well. His CP/M burst into life at 4 MHz, the fridge which caused occasional ‘crashes’ no longer had any effect, spurious noise from other sources no longer corrupted programs, in fact, perfect. We can see how this problem could inhibit correct keyboard function, but as to the rest…​well? Still in desparation this one is worth a try.

When I recently added a Dual Disk System to my Nascom 2, I wanted to be able to switch between various operating options. On the one hand the CP/M system is superb in its file handling capabilities and there is extensive software support. On the other hand, the standard ‘ASM’ and ‘DDT’ utilities are 8080 code handlers, and ‘ED’ is rather clumsy to use when it comes to editing source code. ‘EBASIC’ is quite similar to other 8K Basics in its features, apart from some of the file handling commands, and again, it is necessary to construct source files using ‘ED’. So until I obtain MACRO80, MBASIC and Diskpen and other software more suited to the Z80 CPU and Nascom hardware, there is considerable attractiveness in being able to use ZEAP, NAS-SYS, ROM BASIC, NASDIS, NASPEN, as well as commercial software such as Chess, etc, that I have.

Most of the Nascom software will run in RAM (although you must have the tape version of ZEAP); there is a large number of options available to users on how to map their Nascom, depending on how much RAM or ROM is used and its addressing. The system described in this article is only one way of obtaining a high degree of flexibilty,