---

This is the R.O.M.E.68000 Manual version 0.51.
This is an experimental version.
Copyright © 1997 by G. Mezzetti; last update: January 1, 1999.

Ordinary Instructions of the ``Control'' Class

Jump if Zero, otherwise DeCrement

Mnemonic:

JZDC

Operands:

A,B

Oper.	Addressing Group	Op. Use	Mult. Op.
A	jadr	a	-
B	cadr	e	-

Instruction Key:

62

Formal Description:

if B = 0 then
   @(A) --> IP {jump to A}
else
   B - 1 --> B {decrement B}
end if.

Informal Description

While B is different from 0, this instruction does not perform the jump, but decrements B itself; if B has reached 0, the instruction jumps to A. Please note that operand B allows only a control address, not a destination address.

This instruction works like a ``while ... do ...'' statement, rather than like a``repeat ... until'' one: you should put it at the beginning of the loop it controls, not at the end.

---