Micro­power

For my own purposes, I do not so much require programs to be stored as data. In particular, for one application where I want to use big letters on the screen, I plan to place a 2732 version of the Nascom Character Generator into the spare 4K block and use that in place of the conventional DATA statements that take up an immense amount of storage in BASIC programs to perform this function. I will probably at the same time replace some of the less imaginative graphics, such as the teletext pixel patterns, with a set of subroutines that can be called from BASIC of Assembler programs.

One of the last worries that you may have is that your neat, flexible Nascom is getting ROM bound. There is absolutely no reason why this should happen, as long as you do not want to keep changing from one ROM program to another without switching off.

The full 48k of RAM can easily be accomodated alongside 26K of ROM and EPROM that will fit on the Dual Monitor board and the 2K of RAM on the Nascom 1 board. It cannot, however, be accomodated at the same time and, therefore, a simple switch is neede to disable either the RAM or the ROM. This is simply made with a few TTL chips and installed after the decode block to route the signal to either the RAM or ROM. What normally happens is that the ROM is initially enabled until a signal is sent to switch permanently to the RAM. This in called a Phantom line and is a common signal in S-100 systems. It can either be a decoded port signal or one of the PIO lines, in which case it can be used to toggle the selected chips and possibly alter the addresses – with a bit of logic.

Unless you are content to enable the RAMs once and for all, you should check whether the disabled RAMs are refreshed, if you want to use their contents again anyway.

It is about here that the project gets passed back to you, since my own ideas are getting out of the mainstream of computing and into the specific areas of my interests. If you want to find out about light-pens, Teletext interfaces, piano-keyboards and embroidery designs, then each of these can make up a whale article…​another time though.

I hope that the above has been of use to you if your Nascom 1 was beginning to feel a little restricted and you thought the only way out was a Sinclair. For the price of a Spectrum, you can implement most of the above starting from a standard Nascom 1 and that will just be the start of a male new lease of life.

Routine to relocate BASIC and perform cold start