80-Bus News


September–October 1983 · Volume 2 · Issue 5

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this complexity comes cost. A recent distributors one-off price I have for the Am9511 is £90.00, with the Am9512 at £111.38. (Both 2MHz devices.)

The Am9511 and Am9512 are basically the same processor, and the main difference lies in the way that they are microcoded. The 9511 offers 16-bit and 32-bit integer arithmetic, 32-bit floating point arithmetic, and a variety of derived floating point functions (sine, cos, log etc). The 9512 handles floating point numbers only, and lacks the transcendental functions of the 9511, only offering the four basic functions of + – * /. However the floating point numbers can be either single precision (32-bit), or double precision (64-bit), and all calculations are performed to the proposed IEEE floating point standard [1][2]. (I believe that after fitting that lot in to the Am9512, there was no room left for the microcode to handle the other functions.)

Anyway, all this preamble leads into the review of the Belectra HSA-88B Arithmetic Processor board. This 80-BUS board is based on the Am9511A arithmetic processor, and before we launch into the actual review, a summary of the 9511s instruction set can be found in table 1 for those of you who have never met the device.

NOTE: The 9511 is a stack orientated processor. Operands are first pushed onto the internal stack, and then a command is issued to the processor. TOS stands for Top-Of-Stack, and NOS for Next-On-Stack. The 9511 runs from a 2MHz clock, (but there are more expensive versions at 3MHz – £123.75 and 4MHz – £146.25), and the variation of execution times demonstrates the data dependency of the algorithms used.

The Belectra HSA-88B

What you get:
Submitted for this review was:
1 8x3 pcb with 6 ICs on it.
1 7-page manual + AMD Am9511A data sheet.
1 Hisoft Pascal Manual + 1 disc.


The 8x3 pcb contains just 6 ICs, including the maths processor. I give Belectra full marks for showing restraint over the board, because it is so easy to look at all the spare space available on an 8x8 card, and to start adding CTCs, PIOs, real-time clocks etc, and before you know it the price of the board has gone up by more than £50 for features that most people could do without. Cosmetically the review card differs from the usual 80-BUS standard. Due to the relative simplicity of the circuit, Belectra have opted to produce a single-sided board. As a result there are about two dozen links on the top of the board. It is silk-screened, but there is no solder resist. The overall colour is blue, and it is fitted with a handle to ease extraction. (Mind you appearance isn’t everything, people buy the Ford Sierra and I once owned a Fiat 850.)

The board occupies two I/O ports, which can be selected (via straps) to be 80/81H, 90/91H,....F0/​F1H. The board came already strapped for 80/81H. The Hisoft Pascal worked with it at this address, and no indication is given of how to patch the HP5 compiler to support any of the alternative addresses. No circuit diagram is supplied, but the manual does state that DBDR is not implemented, making the card incompatible with Nascom 1s.

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