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DESCRIPTION OF INSTRUCTIONS
359
99. SUBB A, Rr (Substract register from accumulator with borrow)
10011r2 r1 r0
70
Instruction code
Operation
Number of bytes
Number of cycles
Flags
(PSW)
Description
Example SUBB A, R7
Instruction code
: Byte 1
(A)←(A)–((C)+(Rr)):
C AC F0 RS1 RS0 OV F1 P
•• • •
:
:
:
The carry flag content and the register r contents are
substracted from the accumulator contents. The result is placed
in the accumulator, and the flags are updated.
:
10011111
70
Byte 1
1
1
Before execution After execution
:
Register 7
01011000
70
Register 7
01011000
70
Accumulator
10000100
70
Accumulator
00101011
70
1
Carry flag
0
Carry flag
0
Auxiliary carry flag
1
Auxiliary carry flag
0
Overflow flag
1
Overflow flag