Micro Power 64K RAM Board Review

by S. Weir

I had deliberately waited several months after it was first announced so that, firstly, any bugs would be ironed out before I bought one, and secondly, so that I could read the review of it that was promised in Micropower. Unfortunately, not all the bugs had been found (or they had been left in deliberately to make life more interesting?) and the promised review did not appear. Perhaps it was thought that there was not enough interest in the board – there probably aren’t too many unexpanded Nascom around now I suppose. However, this board makes an inexpensive way to add 64K of RAM and a PCB to a Nascom 1 – total cost about £100. (A Nascom 2 does not require the buffer board to be populated and the cost is about £85.)

The PCB itself is of the highest quality and is worth every penny of the £43 – except for one small point – there is a small piece of track missing, about half an inch long, on the underside of the buffer board section near to the Nasbus connectors. It should connect from the track coming from B17 pin 5 to the Nasbus. Not only does this mess up the addressing of the memory but it also causes havoc with the I/O (ie. keyboard!) since the missing track means that A3 is not connected to B4, the port decoder. You can imagine what fun I had trying to sort that out. This is the only PCB error I found, however, I noticed during my investigations into the track Layout that the DMA daisy chain does not appear to have been implemented (not that it really matters to most people). Instead of going to Nasbus pin 17, /BAO is connected to /BAI near to B13.

On the whole, the manual supplied with the board is very good with clear explanations of the hardware. For those of us with a nervous disposition, do not put the tantalum capacitors in the board the way the instructions say. This results in your lovely new 64K board exuding several puffs of smoke and an obnoxious smell of fried tantalum capacitors! This brings back memories of the Nascom 3A power supply – funny how these designer chaps don’t know their +’s from their –’s.

The instructions for fitting 6116’s to the PCB seem wrong to me – when fitting one 6116 it should be fitted at G1, not G3, otherwise it is sitting on top of the 6576. Also, the instructions say that when fitting two 6116’s to get a full 4K of programmable graphics, the links L1 and L2 should be set up as for 4118’s. I think this is wrong and they should be as described for the 6116. Details are given for switching in the extra 6116 via G7. This disables the 6576. An alternative method is to keep the 6576 enabled and select between 6116’s by taking G6 pin 12 high or low.

The explanation of the memory mapper is, on the whole, clear but I would have liked to know how to map the PCB at 0000 which at the moment I can not see how to do. Also the method given for