17 Apr
2006
17 Apr
'06
5:05 p.m.
> When I was developing Z80-based products, an
ongoing *battle*
> was the use of hex vs. "split octal" (e.g., 0xFFFF -> 0377 0377).
I've worked on a machine where an 8-bit microcode adress was given in
4-digit split octal. That is, something like 1207 for A7 hex.
> The octal camp claimed the Z80 was an "octal
machine" (oh, really?)
I am trying to rememebr, but I _think_ the Intellec MCS8i has the front
panel data switches grouped in 3s (albeit only by white lines on the
panel), even though all the ROM monitor commands use hex
> and, for "proof", showed how so many of
the opcodes could be
> committed to memory just my noting the source & destination
> register "codes" and packing them into an octal representation:
> xx xxx xxx (of course, I wonder how well their argument would
> stand up if Zilog had opted to encode the register fields
> as: xs dds dsx?? :> )
Yes, but they didn't. Many of the simpler (8080) opcodes are easier to
encode in octal...
Would you claim the PDP11 was an octal or hex machine? It's 16 bit (so
hex would be more natural), but I've never seen the machine language
written in anything other than octal (or pure binary, of course). Again,
for many (but not all) instructions, there are 3-bit fields aligned on
octal digit boundaries for things like register selection.
Me, I wish they'd made those common TTL 7-segment
decoder/driver chips
display something more like hex when you got into codes past 9...
I think the display patters for 1010-1111 for the 7447A (I assume that's
one of the chips you were refereing to) came naturally from the logic
used to decode 0000-1001, along with the fact that 1111 should be a
blank. Rememebr when that chip was designed, every gate cost money :-),
it certainly isn't a 16 word * 7 bit ROM.
That said, I think it is a pity there wasn't a later TTL 7 segment
decoder chip (say a 74LS547 or something) that did display 0-F as you
might expect.
-tony