Monitor for iSBC 8024

From: ajp166 <ajp166_at_bellatlantic.net>
Date: Sat Nov 4 12:48:50 2000

From: Eric Smith <eric_at_brouhaha.com>


>Allison wrote:
>> To be exact the z80 has
>[list of registers deleted]
>
>You forgot IFF2. :-)


I know that but consider who most of this is aimed at.

No question the z80 has many more bits than 6502,
8080, 8085, 9900, and a pot load more. Only the 1802
has more stoarge (though simpler elsewhere).

>And both the Z-80 and 6502 have at least one more
>bit that's "sort of" programmer visible, the NMI
>edge-detect flop.


I tried to limit it to the programmer accessable. If
we add temp registers and whole knows what in the
state or microcode portion of the machine it surely
would grow more.

The 6502 distinguished itself in the same fashon as PDP-8.
That is it was simple, cheap to manufacture and had an
adaquate instruction set to do a lot of tasks. it's cheapness
was due to the ease of implementation in silicon.

>
>> 6502
>> SP 9BIT (HIGH BIT =1)
>
>It's either 8 bits, or 16 bits with the high 8 being stuck at
"00000001".
>There's no meaningful reason to consider it a 9-bit register. I
personally
>only find it sensible to count the bits that change, so I call it 8.


Agreed. The 9bit comes from the Osborne view of microprocessors.

>
>> STATUS 8BIT
>
>7 bits, or 8 with one bit stuck high..

same deal. We can consider the unused bit as "reserved".

Allison
Received on Sat Nov 04 2000 - 12:48:50 GMT