<< Previous | Next >>

JR cx,label     Jump Relative     Rabbit 4000/5000 Instruction

Opcode	Instruction	Operation
----	JR cx,label JR cx,mn1	if {cx} PC = PC2 + e
A0 e	JR GT,mn	if {GT} PC = PC + e
B0 e	JR LT,mn	if {LT} PC = PC + e
A8 e	JR GTU,mn	if {GTU} PC = PC + e
B8 e	JR V,mn	if {V} PC = PC + e

1 The 16-bit constant mn is the destination logical address of the jump. 2 The value of PC after the instruction fetch.

Clocks	8-Bit Access	16-Bit Unaligned	16-Bit Aligned
Rabbit 4000	5	n/a	n/a
Rabbit 5000	6	6	6

Flags				ALTD			IOI/IOE
S	Z	L/V	C	F	R	SP	S	D
-	-	-	-

Description

If condition cx is true, this instruction transfers control to the specifed address. The address is specified by a label or logical address. The assembler translates the label or logical address "mn" to an 8-bit signed displacement value, "e".

The displacement value "e" is relative to the address of the first byte of the instruction following JR. This fact is because the processor calculates the new PC value after it increments the PC for the instruction fetch of JR. If condition cx is false, PC is incremented normally.

Condition Code	Flag Bit Value	Description
GT	(Z or (S xor V))=0	True when Z is 0 and L/V and S are either both 1 or both 0.
LT	(S xor V)=1	True when either S or L/V is 1.
GTU	((C=0) and (Z=0))=1	True when C and Z are both 0.
V	L/V=1	True when L/V flag is set: there is overflow.

Note that the relative jump has a limited range of [-128, 127] from the address of the first byte of the instruction following the JR instruction.