CMP 和进位标志

Question

处理器：MSP430 16 位 RISC

有人可以根据下面实际设置进位标志的时间来解释 CMP 指令吗？从手册上说，

CMP(.B) src,dst ..... dst - src

如果src不等于dst，是否会设置进位标志？

cmp    r15, r11
jnc    #1234

Answer 1

用户指南说：

Description
The source operand is subtracted from the destination operand. This is made by adding the 1s complement of the source + 1 to the destination. The result affects only the status bits in SR.
[…]
Status Bits
C: Set if there is a carry from the MSB, reset otherwise

换句话说，如果存在无符号溢出，则设置C。

这在跳转指令中也可以看出：JC(进位跳转)和JHS(高或相同跳转)是同一条指令，JNC(无进位跳转)和JLO(低进位跳转) ).

Example If R5 ≥ R6 (unsigned), the program continues at Label2.
CMP R6,R5        ; Is R5 >= R6? Info to C
JHS Label2       ; Yes, C = 1
...              ; No, R5 < R6. Continue

CMP 和进位标志

CMP and carry flag

assembly

msp430

instruction-set