27 Feb
2008
27 Feb
'08
9:25 p.m.
Christian Corti wrote:
For example SN7439 (NOT '38; equivalent to DEC8881) and SN7489 (16x4 bit
RAM; extensively used in some PDPs for registers).
Hoo boy, you reminded me of The Jones Machine, by one Hillary Jones (no
relation). Published in Byte in the 1980s, a 4 instruction / 8 bit
machine using a 74181 and 7489s. IIRC, one instruction was "store the
1's complement of the register" which was more or less a freebie from
how the 7489s were used.
A project I did for college was expanding it to 16 bit words, four bit
opcode and twelve bits of address, using more modern/common TTL (circa
1987), and adding instructions to support a stack, calling subroutines,
and ...?
Boy, I wonder where the paperwork for that is. Never got around to
trying to build one so it's just a paper design, but something I was
rather proud of at the time.
--S.