8 Mar
2011
8 Mar
'11
8:03 a.m.
At 23:56 -0600 3/7/11, Jules wrote:
Yes, that seems to be the 'famous' one that
gets mentioned everywhere. It
seems it was of the shift-add variety. Anyone recall if it would work with
signed integers? (I'm just trying to work out how the math works for signed
multiplies at the moment)
I have a scanned .pdf of the 6809 programmer's manual here,
happy to send out if anyone wants it, but it's 12.8 MBytes. (I got it
from the freescale website, since reorganized; it's
online at
http://www.maddes.net/m6809pm/ .)
It says the MUL instruction A x B -> D (unsigned) takes 11
MPU cycles. ADD instructions take a minimum of 2 cycles, as do shift
(roll, etc) instructions. So I think maybe there must have been some
silicon (vs. microcode) involved in the multiply? I don't see how the
shift-add sequence could be done in only 11 cycles.
MUL is unsigned arithmetic only.
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