baum@Apple.COM (Allen J. Baum) (07/22/88)
[]
The original HP2116 was designed by a company that was bought by HP, I believe.
(Digital something-or-other, but not "Equipment Corp").
Its instruction set is a direct ripoff, in almost EVERY respect, of the PDP8.
The instruction word was extended to 16 bits, which gave an extra bit for
op-code, an extra bit for accumulator specification (it had 2), and 2 extra
bits for address offset. Like the PDP-8, it had no subtract instruction. You
had to negate and add. Like the PDP-8 it had an operate instruction. Unlike
the PDP8, it had two separate, identical shift fields, instead of a bit to
say shift twice. The I/O system is pretty similar. And so on...
The original 2116 was built with CML logic, a kind of crude ECL. The 2116
ran very fast for its day; its sucessors were not as fast as the original.
The packaging was amazing- it could take a LOT of punishment, and keep on
ticking. This is part of the reason HP has a reputation for reliability.
The I/O system on the HP21xx was fairly simple; read or write, and strobe a
bit or two while you where at it. The I/O addresses were pre-decoded at each
slot; a six bit I/O address went through two 3->8 decoders, and these decoded
outputs were distributed to each card in an x-y matrix fashion, so an 'and'
gate on each card was sufficient for address recognition. Actually, two sets
of decoded addresses were distributed, so that a card could recognize two
consecutive addresses. This is so that complex I/O devices could occupy two
slots, but have the same address. This pre-decoded I/O scheme is what led to
the Apple II I/O structure.
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{decwrl,hplabs,ihnp4}!nsc!apple!baum (408)973-3385pete@octopus.UUCP (Pete Holzmann) (07/23/88)
I don't remember whether the HP 21xx series had its origins at Stanford.
I was there slightly too late for that. davel@sequent remembers, I'm sure.
What *was* interesting was that some folks at Stanford got sick of the
stackless operation, so they added one! Made things a lot nicer. Too bad
it didn't get into the 'real' product.
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