This is an attempt to list all “official” firmware related to the Nascom computers.
If anyone has anything to add, please let me know!
The Monitor programs were stored in EPROM and were used much as a PC BIOS is used today, but with its own command line interface built in. Several versions were produced.
| NASBUG 1.T1 Monitor | The first monitor. Soon superseded. |
| NASBUG 1.T2 Monitor | Successor to the above. |
| NASBUG 4 Monitor | Successor to the above. |
| NAS-SYS Monitor | Successor to the above. Provided with the Nascom-2 |
| NAS-SYS 3 Monitor | Successor to the above. |
| NAS-SYS Tool Kit | Addition to NAS-SYS. |
| NASCOM TINY BASIC | A programming language. |
Monitor Programs
Throughout its relatively short life the Nascom family spawned several good monitor programs. Each had its strengths and its weaknesses. All the monitors were written by the same person, Richard Beal (including B-BUG – and no, not the Netscape bloke, please don’t bother him with this. I already asked!).
NASBUG 1.T1
This was the first monitor produced and, I am told, was completely hand coded from mnemonics into hex for the programmer. It then ran almost faultlessly first time. That is quite a feat in a thousand bytes of machine code!
Taking a risk with copyright law, I have included the listing from the software manual for this monitor (not for any of the others though). I feel that the risk is worthwhile in this case as this monitor is probably of no use whatever today! It is very instructive to follow the listing though.
I have deliberately left the scans large so that you can print them out onto A4 paper, although you may need to rotate them through 90 degrees first. (Incidentally, I did try to use some character recognition software that came with the scanner to produce a straight text file but it fell over on the multiple columns.)
Note that this is the original NASBUG monitor, it doesn’t have a lot of the trimmings of the later programs and it does have bugs. However, it is ideal for this purpose as the listing is clear and relatively short.
NASBUG 1.T2
Supplied with all kits from July 10th 1978, this fixed a problem that resulted in a high number of errors when loading a cassette. There was also a slight mod to the keyboard look-up table. It was still supplied on a single 2708 EPROM (1k x 8 ) and became the standard for 1k monitors.
B-BUG
A “third-party” monitor (not a NASCOM product) released in 1978 that added a second, partly used, EPROM to NASBUG to give some additional commands. B-BUG came with a very nice little manual that included a commented assembler listing of the second EPROM and a list of the changes made in the original NASBUG EPROM. It had a major advantage over previous monitors, new cassette routines that were four times faster than what we had been used to. Another nice extension was the facility to access the whole of the Nascom’s meagre character set via the keyboard.
DJ-BUG
This is an oddball. I don’t know who produced it but it made life easy for some machine code programmers by providing a simple interface to the REVAS disassembler. I am certain that it wasn’t an “official” monitor release, I mention it here just for completeness. It also incorporated search commands to look for single and double byte commands/data. It included the “fast” R and W tape routines that had appeared in B-BUG. I think it was distributed through INUC (see reference on Software page) but I am not sure. I don’t have a copy of this monitor but I suspect it was just a bit of code patched into the second B-BUG EPROM to give the additional commands.
NASBUG-4
Released by Nascom Microcomputers in February 1st 1979 (the first formal issue date of my manual). The last monitor in the NASBUG line, this was a 2k system supplied in 2 1k EPROMs. It introduced many new routines – a lot of them were based on the B-BUG changes. This monitor was a direct upgrade on T2 and ran just about all the existing software. It also included support for (and the ability to act as) an ASCII terminal connected to the serial port. This proved to be the best monitor so far and became very popular.
NAS-SYS 1
Dated March 24th 1980 in my manual, this was the “new” monitor that was fitted to the Nascom-2. Although Nascom-1 users were eventully encouraged to upgrade, Nascom did not make it available for separate sale for some months after its release. It was designed to be expandable – the user could add routines to the monitor and, in some cases, replace routines with user code. This made a very powerful system but now it took up a 2k ROM. Copies soon appeared on 2 1k EPROMs for the Nascom-1 users. Unfortunately, the re-arrangement of the monitor code meant that many existing NASBUG programs would no longer run without modification. Many Nascom-1 user “piggy backed” both monitors and switched between them – just flick the switch & press Reset!
NAS-SYS 2
This is very much an unknown quantity to me. I don’t remember ever seeing it and it may never have been officially released. Please let me know if you have any details!
NAS-SYS 3
Several improvements over NAS-SYS 1 resulted in this, what I think is the final standard monitor. This also came with full documentation. I have included page 1 and page 2 here. It is interesting that the book makes no mention of this being an upgrade to NAS-SYS 2. Only NAS-SYS 1 is mentioned.
There was also, eventually (1983), a third 1k EPROM which could be added to NAS-SYS monitors. This was named SYS-EX, but apart from this I know little about it.
Incidentally, there was also a machine code monitor built into the Camputers Lynx machine, a normal console type built many years ago in Cambridge, UK. It was started by the command MON in BASIC. I suspect that this was the last home computer to have such software in ROM.
nascom.info 
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