Echelon Neuron - Manual (Page 91)

DBRNZ (Decrement and Branch If Not Zero)
The DBRNZ instruction performs two functions: it decrements the unsigned 8-
bit value on the top of the return stack and performs a conditional branch. The
DBRNZ instruction uses the indirect addressing mode for the comparison and
the relative addressing mode for the branch operation. If the result of the
decrement is not zero, the instruction branches to the destination indicated by
the displacement value, which must be in the range -126 to +129. If the value on
the top of the return stack becomes zero, the DBRNZ instruction drops the value
from the return stack and continues processing with the next instruction. TOS is
not affected by this instruction.
The displacement expression must resolve at link time to a value in the range -
128 to +127 (two less than the actual displacement because the displacement
calculation includes the size of the DBRNZ operation itself).
The Neuron Assembler also supports the use of a label for the displacement
expression; manual calculation of the displacement value is not required.
The DBRNZ instruction applies to Series 3100, 5000, and 6000 devices.
Syntax:
The DBRNZ instruction requires a single operand to specify the displacement:
DBRNZ displacement
Table 26 describes the attributes of the DBRNZ instruction.
Table 26. DBRNZ Instruction
Instruction Hexadecimal
Opcode
Instruction
Size (Bytes)
CPU Cycles
Required
Affect on
Carry Flag
DBRNZ 70 2 5 None
Example:
The following example calls a function named do_it repeatedly, until the value n
on the return stack is zero. Thus, this example implements a do until loop
construct. This example assumes that the called function resides at a high
memory address or is a system function.
Example APEXP ; ( n -- )
poppush ; ( ) R(n)
loop_body ; ( ) R(n)
callf do_it ; ( ) R(n)
dbrnz loop_body ; ( ) R({n})
ret ; ( ) R( )
Neuron Assembly Language Reference 81