S3F84B8_UM_REV 1.00 6 INSTRUCTION SET6-756.3.63 SBC — SUBTRACT WITH CARRYSBC dst,srcOperation: dst dst – src – cThe source operand, along with the current value of carry flag, is subtracted from the destinationoperand. The result is stored in destination. The contents of source remain unaffected.Subtraction is performed by adding the two’s-complement of source operand to destinationoperand. In multiple precision arithmetic, this instruction allows the carry (“borrow”) fromsubtraction of low-order operands to be subtracted from subtraction of high-order operands.Flags: C: Set if a borrow occurred (src dst); 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 sign and the signof result is same as the sign of source; cleared otherwise.D: Always set to “1”.H: Cleared if there is a carry from the most significant bit of low-order four bits of the result;set otherwise, indicating a “borrow”.Format:Bytes Cycles Opcode(Hex)Addr Modedst srcopc dst | src 2 4 32 r r6 33 r lropc src dst 3 6 34 R R6 35 R IRopc dst src 3 6 36 R IMExamples: Given R1 = 10H, R2 = 03H, C = “1”, register 01H = 20H, register 02H = 03H, and register 03H =0AH:SBC R1,R2 R1 = 0CH, R2 = 03HSBC R1,@R2 R1 = 05H, R2 = 03H, register 03H = 0AHSBC 01H,02H Register 01H = 1CH, register 02H = 03HSBC 01H,@02H Register 01H = 15H,register 02H = 03H, register 03H = 0AHSBC 01H,#8AH Register 01H = 95H; C, S, and V = “1”In the first example, if working register R1 contains the value 10H and register R2 contains thevalue 03H, the statement “SBC R1,R2” subtracts the source value (03H) and the C flag value(“1”) from the destination (10H) and then stores the result (0CH) in register R1.
