Review of the Belectra Arithmetic Processor Board.

by IJC

A common problem with micros is their lack of speed and accuracy when it comes to calculations. For the average user, the fact that a figure is only accurate to the 6th decimal place may be rather trivial but when it comes to complex graphics calculations or financial formulae the effects can be compounded to make the figures unacceptable. Also, when calculating trigonometric functions in a program, (commonly used in graphics plots again) speed is very important. The time taken to calculate the LOG of a number is horrendous when compared to the rest of the program. One way round this is to use look up tables but this uses up a lot of memory and isn’t very accurate.

The answer, as far as the Nascom is concerned, has come in the form of the Belectra HSA-88B Arithmetic Processor board.

The board (or at least the one I loaned for review arrived well packaged and in silver paper. I also received a rather thin manual and a data booklet on the AM9511A processor (the heart of the board). The board isn’t a full size 8x8 board but it is blue. (This seems to be coming the Nascom industry standard colour.) The board doesn’t look as polished as some of the other Nascom boards available but it was adequate and who cares if it doesn’t look pretty anyway.

Even for its small size, the board is only sparsely populated and at £199 you may wonder what you are paying for. The answer is, the AM9511 processor. It does account for a rather large chunk of the total cost.

The board is supplied ready wired to a default port and with a default clock speed which most users should not need to change. However, by means of wire links, you can select which two ports you want to address the board on (80/81H, 90/91H, A0/A1H, B0/B1H, C0/C1H, D0/D1H, E0/E1H or F0/F1H) and you may have to change the link on the clock speed if you are running a 2MHz Nascom. Clean, simple and straight-forward. The board does not support DBDR so it is incompatible with the Nascom 1 which seems a shame with so many still being in use.

The arithmetic processor works totally independently of the Nascom Z80 and is accessed via 2 I/O ports. To use the processor couldn’t be simpler. The 9511 contains a stack, a command register and a status register. The data to be operated on is firstly pushed onto the stack (always least significant byte first), a command byte is sent to the command register (eg. 16-bit multiply – 6EH), the Nascom then waits for the arithmeic to finish (by testing the status port) and then it reads the result from the stack port again (most significant byte first this time). One example that they give in the manual is a follows:–