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INSTRUCTION SET
S3C84MB/F84MB_UM_REV1.00
SUB — Subtract
SUB
dst,src
Operation:
dst ← dst – src
The source operand is subtracted from the destination operand and the result is stored in the
destination. The contents of the source are unaffected. Subtraction is performed by adding the
two's complement of the source operand to the destination operand.
Flags:
C: Set if a "borrow" occurred; cleared otherwise.
Z: Set if the result is "0"; cleared otherwise.
S: Set if the result is negative; cleared otherwise.
V: Set if arithmetic overflow occurred, that is, if the operands were of opposite signs and the
sign of the result is of the same as the sign of the source operand; cleared otherwise.
D: Always set to "1".
H: Cleared if there is a carry from the most significant bit of the low-order four bits of the
result; set otherwise indicating a “borrow”.
Format:
opc
opc
opc
Examples:
dst | src
src
dst
dst
src
Bytes
Cycles
Opcode
(Hex)
2
4
22
r
r
6
23
r
lr
6
24
R
R
6
25
R
IR
6
26
R
IM
3
3
Addr Mode
dst
src
Given: R1 = 12H, R2 = 03H, register 01H = 21H, register 02H = 03H, register 03H = 0AH:
SUB
SUB
SUB
SUB
SUB
SUB
R1,R2
R1,@R2
01H,02H
01H,@02H
01H,#90H
01H,#65H
→
→
→
→
→
→
R1 = 0FH, R2 = 03H
R1 = 08H, R2 = 03H
Register 01H = 1EH, register 02H = 03H
Register 01H = 17H, register 02H = 03H
Register 01H = 91H; C, S, and V = "1"
Register 01H = 0BCH; C and S = "1", V = "0"
In the first example, if he working register R1 contains the value 12H and if the register R2
contains the value 03H, the statement "SUB R1,R2" subtracts the source value (03H) from the
destination value (12H) and stores the result (0FH) in the destination register R1.
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