Instruction Set
4-84
JBE
Jump If Below or Equal
JBE
JNA
Jump If Not Above
What It Does
If the previous instruction sets the Carry Flag (CF) or the Zero Flag (ZF), JBE and JNA stop
executing the current sequence of instructions and begin executing a new sequence of
instructions; otherwise, execution continues with the next instruction.
Syntax
Description
JBE and JNA test the flags set by a previous instruction. The terms
above and below
indicate an unsigned number comparison. If the given condition is true, a short jump is
made to the location provided as the operand.
Operation It Performs
Flag Settings After Instruction
Form
Opcode
Description
Clocks
Am186 Am188
JBE
rel8
76
cb
Jump short if below or equal (CF=1 or ZF=1)
13,4
13,4
JNA
rel8
76
cb
Jump short if not above (CF=1 or ZF=1)
13,4
13,4
JBE
label
To jump if the result of a previous
unsigned comparison was below or
equal
, use JBE or its synonym, JNA.
Both forms perform the same operation.
JNA
label
if ((CF == 1) || (ZF == 1))
{
/* extend sign of label */
if (
label < 0)
displacement = 0xFF00 |
label;
else
displacement = 0x00FF &
label;
/* branch to labeled instruction */
IP = IP + displacement;
}
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
–
–
–
–
–
– res – res – res –
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...