Rev. 1.50, 10/04, page 328 of 448
10.1.73 SUBC (Subtract with Carry): Arithmetic Instruction
Format Operation Instruction Code Cycle T Bit
SUBC Rm,Rn Rn - Rm-T → Rn, borrow
→ T
0011nnnnmmmm1010 1 Borrow
Description: This instruction subtracts the contents of general register Rm and the T bit from the
contents of general register Rn, and stores the result in Rn. A borrow resulting from the operation
is reflected in the T bit. This instruction is used for subtractions exceeding 32 bits.
Notes: None
Operation:
SUBC(long m, long n) /* SUBC Rm,Rn */
{
unsigned long tmp0,tmp1;
tmp1 = R[n] - R[m];
tmp0 = R[n];
R[n] = tmp1 - T;
if (tmp0<tmp1) T = 1;
else T = 0;
if (tmp1<R[n]) T = 1;
PC += 2;
}
Example:
CLRT ;R0:R1(64 bits) – R2:R3(64 bits) = R0:R1(64 bits)
SUBC R3,R1 ;Before execution T = 0, R1 = H'00000000, R3 = H'00000001
;After execution T = 1, R1 = H'FFFFFFFF
SUBC R2,R0 ;Before execution T = 1, R0 = H'00000000, R2 = H'00000000
;After execution T = 1, R0 = H'FFFFFFFF
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