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A-7
INSTRUCTION SET REFERENCE
All of the bit instructions in the MCS 251 architecture (Table A-7) have opcode A9, which serves
as an escape byte (similar to A5). The high nibble of byte 1 specifies the bit instruction, as given
in Table A-10.
Table A-10. Bit Instructions
Instruction Byte 0(
x
) Byte 1 Byte 2 Byte 3
1 Bit Instr (dir8) A 9
xxxx
0 bit dir8 addr rel addr
Table A-11. Byte 1 (High Nibble) for Bit Instructions
xxxx
Bit Instruction
0001 JBC bit
0010 JB bit
0011 JNB bit
0111 ORL CY,bit
1000 ANL CY,bit
1001 MOV bit,CY
1010 MOV CY,bit
1011 CPL bit
1100 CLR bit
1101 SETB bit
1110 ORL CY, /bit
1111 ANL CY, /bit