RCA COSMAC User Manual page 32

COSMAC Microprocessor
(cont'd)
M ADDRESS M BYTE
OPERATION COMMENTS
010A F4
D+M(R(3)) Add
in
multiplicand.
010B 33
BDF
J
If carry in D F, branch to
010C 10
loc 0110; otherwise:
010D
F6 D/2 Shift the result right
I
010E 30 BR
J
and go to 0113 to shift the rest
010F 13 of result.
0110 F6 D/2 Shift result right.
0111
F9
D OR immed
J
OR in high bit for carry
0112 80
(data)
from instruction at 010A (NOTE).
0113 B4
D~R(4).1 Store result back.
0114
84
R(4).~D Fetch low byte of result.
0115 33 BDF
}
Delayed branch on shift in
0116 lA 010D or 0110, to 011A.
0117 F6 D/2 Shift low byte
I
0118 30 BR
}
and branch to 001 D
0119 10 to finish shift.
011A F6 D/2 Shift low byte,
011B F9
D OR immed
]
and OR in high bit
011C 80
(data) from shift of 010D or 0110 (NOTE).
011D A4
D~R(4).0 Put low byte back.
011E 3B BNF
]
Branch back ("loop") if the original
011F
04 80 hasn't shifted thru yet.
0120 Product is now ready. Continue to
rest of program.
NOTE: The SHIFT RIGHT instruction will not shift the DF bit into the highest bit of D. These operations
essentially restore, if DF=l, a "1" bit into the highest bit of D after a SHI FT RIGHT.
Fig. 40 - Example of program for multiplying two bytes and adding the
result to a third byte.
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