80-Bus News


November–December 1983, Volume 2, Issue 6

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By C. Blackmore

My regular reader has probably already noticed that I am constantly extending and improving the noble Marvin, in an effort to build up the biggest and best computer in town. After all, it is very well known that without such a machine available to flash lights and spin great big empty tape reels round and round, the best laid world domination plans are doomed to failure…

My latest addition to the amazing Marvin is the HSA-88B arithmetic processor board from Belectra. The board was originally advertised in this magazine, at £199. However, you will be sad to hear, this price no longer applies. I quote from a letter Belectra sent me – “Since our advertisement in 80-BUS News, we have reviewed our marketing policy (which used to be direct sales to the public) and are now selling also via computer retailers. The price of the HSA-88B has therefore been increased to include dealer margins and other factors associated with selling to trade customers, to £253 plus VAT.” So, if you rushed out and ordered one as soon as you saw the advertisement, you are now feeling pretty pleased with yourself, I expect.

There was going to be a great deal of talk about the hardware you get for the money, here, but a certain David Parkinson stole my thunder in the last issue, so I am frantically re-editing this article to save wasting space by going over old ground. So if it reads as though I have done a rush job, you will know why. I don’t really feel bitter about this, David, honest! Your article doesn’t say how much you paid for your board, was it a freebie?) [Ed.– it was on loan for review and has now been returned to Belectra.]

As processor chips go, the 9511 is fairly odd (though it is by no means as unbelievably bizarre as the old SC/MP chip in Sinclair’s original computer, the amazing MK14) as it does not fetch opcodes and data from memory for itself. Instead, your main processor loads data into the chip, followed by an instruction opcode. When the 9511’s status line indicates that the processing has been done, the main processor can read out the answer. The 9511 has an eight bit bus system for communication with the outside world. Since it deals with either 16 or 32 bit quantities, data has to be sent in two or four byte blocks, and the fast Z80 block output instructions can be used. The chip has five distinct groups of instruction codes, which are for 16 bit fixed point operations (integers), 32 bit fixed point operations (enormous integers!), 32 bit floating point primary and derived operations, and data and stack manipulation operations. The 16 bit and 32 bit fixed point operations that can be performed are addition, subtraction, multiplication and division. The same four operations can also be done in 32 bit floating point format, and these are referred to as the primary operations. The derived operations consist of those that can be built up using the primary operations in various combinations, and are square roots, sines, cosines, tangents, inverse sines, inverse cosines, inverse tangents, common logarithms, natural logarithms, “e” raised to a given power, and any number raised to a given power. If you didn’t understand that sentence, I suggest you try the Open University course, M101, that I recently finished (I am not claiming to have passed, as I don’t believe in tempting providence!) The data and stack manipulation commands are mainly concerned with matters such as changing to and from floating point format, changing sign and so on, but also allow you to load pi into the processor in an amazing 16 clock cycles. If you are into that sort of thing, you might like to work out how many clock cycles it would take to load pi from the main processor to the chip, assuming you know the 32 bit floating point value of pi, which I seem to have forgotten…

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