DEC -- Decrement by 1

DEC -- Decrement by 1 Opcode Instruction Clocks Description FE /1 DEC r/m8 2/6 Decrement r/m byte by 1 FF /1 DEC r/m16 2/6 Decrement r/m word by 1 DEC r/m32 2/6 Decrement r/m dword by 1 48+rw DEC r16 2 Decrement word register by 1 48+rw DEC r32 2 Decrement dword register by 1 Operation DEST = DEST - 1; Description DEC subtracts 1 from the operand. DEC does not change the carry flag. To affect the carry flag, use the SUB instruction with an immediate operand of 1. Flags Affected OF, SF, ZF, AF, and PF as described in Appendix C. Protected Mode Exceptions #GP(0) if the result is a nonwritable segment; #GP(0) for an illegal memory operand effective address in the CS, DS, ES, FS, or GS segments; #SS(0) for an illegal address in the SS segment; #PF(fault-code) for a page fault Real Address Mode Exceptions Interrupt 13 if any part of the operand would lie outside of the effective address space from 0 to 0FFFFH Virtual 8086 Mode Exceptions Same exceptions as in Real Address Mode; #PF(fault-code) for a page fault