8080 Trainer - more info

From: Captain Napalm <spc_at_armigeron.com>
Date: Tue Apr 21 20:06:44 1998

It was thus said that the Great Tony Duell once stated:
> > panel monitor used an octal keypad & display, and the octal thinking carried
> > over to the assembler package. Heath also used "split octal" in the fashion
> > you describe, so that
> >
> > 0110100110101111B (binary)
> > 69af (hex)
> > 64657Q (octal)
> > 151257A (split octal)
> >
> > are all equivalent. if you've never seen it before you'd swear this is a
> > dumb idea, but it grows on you!
> Actually I think Octal is a dumb idea for 8 or 16 bit processors :-) -

  But oddly enough, if you look at the 8080 instruction set through octal
eyes, it makes sense. Heck, the 8086 instruction set as see through octal
eyes makes it look sensible. Of course, most book will show the opcodes as
hexidecimal and that makes it look rather ugly.

> apart from the PDP11, of course, where bit-fields end on 3-bit boundaries
> so it's easy to decode octal instructions in your head...

  Although hexidecimal is very suited for the VAX though. I'm sure once you
get the hang of the common instructions and the address modes, you could
read a hex dump of VAX code.

> I've just thought. In some microcode binary formats it was common to list
> the instructions not in octal, or in hex, but in (say) hex with each
> digit corresponding to a bit field in the word. Suppose you had

  [ snip ]

> Did any machine languages ever write the opcodes like that, I wonder?

  No, but for some machines it would make sense (say, for the 68k, where
most instuctions follow a 4:3:3:3:3 format)

  -spc (Which makes it almost, but not quite, nice for octal)
Received on Tue Apr 21 1998 - 20:06:44 BST

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