AMD Am186 Series, Instruction Set

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Instruction Set 4-87
JCXZ Jump If CX Register Is Zero JCXZ
What It Does
If the previous instruction leaves 0 in CX, JCXZ stops executing the current sequence of
instructions and begins executing a new sequence of instructions; otherwise, execution
continues with the next instruction.
Syntax
Description
JCXZ tests the CX register modified by a previous instruction. If the given condition is true
(CX=0), 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
JCXZ
rel8
E3
cb
Jump short if CX register is 0 15,5 15,5
JCXZ label
To jump if CX is 0, use JCXZ.
if (CX == 0)
{
/* 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 –