Datasheet

Instruction Set Description

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4.6.2.29 JN

JN Jump if negative

JN label

Syntax

Operation If N = 1: PC + (2 × Offset) → PC

If N = 0: execute following instruction

Description The negative bit N in the SR is tested. If it is set, the signed 10-bit word offset contained

in the instruction is multiplied by two, sign extended, and added to the 20-bit program

PC. This means a jump in the range -511 to +512 words relative to the PC in the full

memory range. If N is reset, the instruction after the jump is executed.

Status Bits Status bits are not affected.

Mode Bits OSCOFF, CPUOFF, and GIE are not affected.

Example The byte COUNT is tested. If it is negative, program execution continues at Label0. Data

in lower 64KB, program in full memory range.

TST.B &COUNT ; Is byte COUNT negative?

JN Label0 ; Yes, proceed at Label0

... ; COUNT >= 0

Example R6 is subtracted from R5. If the result is negative, program continues at Label2. Program

in full memory range.

SUB R6,R5 ; R5 - R6 -> R5

JN Label2 ; R5 is negative: R6 > R5 (N = 1)

... ; R5 >= 0. Continue here.

Example R7 (20-bit counter) is decremented. If its content is below zero, the program continues at

Label4. Program in full memory range.

SUBA #1,R7 ; Decrement R7

JN Label4 ; R7 < 0: Go to Label4

... ; R7 >= 0. Continue here.

192

CPUX SLAU144J–December 2004–Revised July 2013

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