
Instruction Set
4-48
DEC
Decrement Number by One
DEC
What It Does
DEC subtracts 1 from an integer or an unsigned number.
Syntax
Description
DEC subtracts 1 from the operand.
Operation It Performs
Flag Settings After Instruction
Form
Opcode
Description
Clocks
Am186 Am188
DEC
r/m8
FE
/1
Subtract 1 from r/m byte
3/15
3/15
DEC
r/m16
FF
/1
Subtract 1 from r/m word
3/15
3/19
DEC
r16
48+
rw
Subtract 1 from word register
3
3
DEC
minuend
/* decrement minuend */
minuend = minuend - 1;
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
Processor Status
Flags Register
reserved
OF DF
IF TF SF ZF
AF
PF
CF
? = undefined; – = unchanged
OF=1 if result larger than destination operand
OF=0 otherwise
AF=1 if carry or borrow to low nibble
AF=0 otherwise
PF=1 if low byte of result has even number of set bits
PF=0 otherwise
–
–
–
res
res
res –
SF=1 if result is 0 or positive
SF=0 if result is negative
ZF=1 if result equal to 0
ZF=0 if result not equal to 0
Содержание Am186 Series
Страница 1: ...Am186 and Am188 Family Instruction Set Manual February 1997...
Страница 10: ...Table of Contents x...
Страница 18: ...Programming 1 8...
Страница 40: ...Instruction Set Listing 3 14...