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SX Embedded Controller Instruction

DJNZ fr,addr

Description: Decrement fr , jump if not zero
Operation: -- fr == 0 ? PC = addr
Flags affected: none
Registers affected: fr PC
Sources referenced: fr
Cycles: 2 *
Opcode:
Actually compiles to: decsz fr; jmp addr
Microchip PIC syntax: DECFSZ fr,1; GOTO addr
Notes:

Guenther says:

DJNZ fr, addr is a so-called "compound" statement, i.e. the SX does not "understand" it directy. Instead, the Assembler generates two subsequent instructions as replacement:

DECSZ fr
JMP addr

In case you specify $ for addr, the Assembler is clever enough to replace $ with the address of the DECSZ instruction, and not with the address of the JMP instruction which would not make too much sense.

The same is true for an argument like $-2, IOW, the Assembler always replaces $ with the address of the first instruction of a compound statement.

BTW, a good method to test the behavior of certain instructions is writing a simple program, and then single-stepping it with the debugger to see what happens.

See also:


file: /Techref/scenix/inst/djnzfraddr.htm, 2KB, , updated: 2004/10/8 11:45, local time: 2017/11/24 04:49,
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