71B vs 75D

[J-F Garnier]

(04-15-2021 11:10 AM)Martin Hepperle Wrote:  In my view, the Capricorn CPU is remarkable technology and the 75 is an interesting bridge between the pocket calculators and the Series-80 desktop computers.
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I think the CPU it is underestimated - one has to compare with CPUs like 8080, Z80, 6809, 6502 and the like.

For its time, the CPU offers some very innovative features, the only drawback in my view is that it did not provide multiplication and division op codes.

On the other hand, which CPU from this era gives you a large set of 16 and 64 bit registers and almost symmetric (all opcodes allowed with all registers) operations?

I concur. I discovered the Capricorn CPU with the Series 80 Assembler ROM (around 1982-1983), and found it very powerful, with its indirect/indexed addressing modes and the capability to operate on 1 to 8 bytes with a single opcode.

One weakness of the Capricorn was the lack of relative call and long jump, requiring to use the index addressing mode to build relocatable (position-independent) code as needed for LEXs, using one register and extra overhead. But I believe this didn't affect the overall performance so much.

I don't see where the Capricorn architecture comes from. It doesn't come from the calculator CPU family, nor the HP desktop computer CPUs. Strange that such CPU was designed from scratch by a calculator division (Corvallis) for the Series 80.
In contrast, the Saturn architecture clearly comes from the Coconut and predecessors.
Any information on the origin of the Capricorn?

J-F