80-Bus News


January–February 1983, Volume 2, Issue 1

Page 29 of 56

Doctor Dark’s Diary – Colour Supplement Edition.

The MAP 80 RAM board.

It was getting to be about time someone brought out a new 80-BUS board that would astound the plastic box brigade, and suddenly there are two around, both containing massive amounts of memory. The MAP 80 board is first on the agenda, simply to make you wonder what the other one is until you get to the appropriate page, although I have put a really subtle clue in the heading. You have seen the advertisements, so you know that the MAP 80 board can hold up to 256K of memory. You may even have seen a hardware review somewhere, that went on about the sheer amazing blueness of the board. So I am going to write about how I went about putting mine together, and the software that is supplied for it. Mind you it is very, very blue...

First of all, being the adventurous type, I ordered the bare printed circuit board, which costs £42-50. The day after I sent the order, I was telephoned by MAP 80, who wanted to make sure that I was not trying to use the board with a Nascom 1. Apparently, this is a combination that does not work! So, I reassured them that I was now using a Nascom 2, and the board arrived very soon after. The board is of a high standard, nice solid glass fibre, with the blue solder resist, and the usual silk screening to show where things should be put. Things are pretty closely packed, as you would expect, since there are fifty four DIL sockets to fit on the board. With the board were the parts list and construction instructions. I ordered all the sockets, resistors, capacitors and most of the TIL chips from Maplin, who managed their usual rapid response. A couple of the chips needed are not mentioned in the Maplin catalogue, but can be obtained from other firms, such as Watford Electronics, or Technomatic. When I unpacked the sockets, I was surprised to find that they were made from a rather nice shade of pale blue plastic, instead of the usual black. When these had been soldered to the blue pcb, the result looked like something from another dimension, after years of looking at green boards with black sockets! Cost of components (excluding PCB and RAMs) was under £20, just! The next step, which I am still saving up for, is to buy the thirty two RAM chips the board can carry. As these are about £4-50 each, the 256K board can be built for just over £200, which is a lot cheaper than people with S100 based computers seem to pay for their boards. The chips have now begun the gradual slide down to a more sensible price, so it is nice to know that the board will work with just a single row to start with, as long as you don’t connect up the chip select lines for rows that are not there.

There may well be murmurs of “What on earth can you use it for?” in the ranks. At first, I used to find a 1K Nascom 1 big enough. Now my programs are much bigger, but there is as yet little probability that I will overflow the 64K mark! No, the magic phrase that made me so keen to get the board was “virtual disk”. [Ed. – see R. Beal’s article elsewhere on VDs (oops!).] And you don’t have to mess around modifying CP/M, because MAP 80 will do it for you. They have done this for me, and the disk has been returned with two new versions of MOVCPM on it, one for the usual display and one for use if you have an IVC card on your system. The source code for the revised BIOS is supplied, which is a very sensible approach, enabling even further customisation of the software without any need to guess what their bit is doing. [Ed. – I wonder how Gemini feel about other manufacturers modifying their CP/M BIOSs and sending out source listings! Naughty!] No doubt, sooner or later, I will have time to have a look how it works! The CP/M works in the usual way when there is 64K or less of memory connected, but when there is more the sign on message will announce that the virtual disk is available, and give its size, according to the documentation. Must order some RAM chips... As a bonus, my “old” 64K, GM802, card is not made redundant by all this. The instructions supplied with the MAP 256 tell you how to fix it so that the software will use it as well. Presumably, the effect of the modifications is, in part, to change the GM802’s paging control port to £FE, from

This is an OCR’d version of the scanned page and likely contains recognition errors.

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