Review of the Belectra Arithmetic Processor Board.
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
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
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