3 May
2004
3 May
'04
6:09 a.m.
One other peculiarity I do remember about the BPC instruction set was that
as it had byte addressing, the byte select was the _most_ significant
bit of a
16-bit address, so that the indirect addresses were only one level -- that
is, you could do indirect addressing through one target word -- this is in
contrast to the 2100 instructions where the most significant bit was used as
an indirection bit indicating a chain of indirect addresses...
Bill
Bill McDermith wrote:
Jay West wrote:
A combination of 2100 and 21MX instruction sets?
Umm... the 21MX is
just a
superset of 2100?
Correct, but if my memory isn't completely gone, it had some
of the 21mx instructions, some of the additional registers, like
the amusing but less useful index registers, but not all of the
21MX instructions, and some of the ones that were included weren't
implemented in the same way (or with the same bit pattern? Can't
remember...) -- It seems to me that you couldn't just use a
21MX compiler to target a BPC, for example.
It's just hard to remember, programmed it every day for a year
in 1980, then moved on to the displays division in Colorado
Springs, and never messed with it again...
Bill McDermith