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SETUSR     Set User Mode     Rabbit 3000A/4000/5000 Instruction

Opcode	Instruction	Operation
ED 6F	SETUSR	SU={SU[5:0],0x01}

Clocks	8-Bit Access	16-Bit Unaligned	16-Bit Aligned
Rabbit 3000A/4000	4	n/a	n/a
Rabbit 5000	4	4	2

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

Description

The System/User Mode Register, SU, is an 8-bit register that forms a stack of the current processor mode and the previous 3 modes. SETUSR shifts the contents of SU 2 bits to the left, then sets bit 1 to 0 and bit 0 to 1, signifying user mode.

This is a chained-atomic instruction, meaning that an interrupt cannot take place between this instruction and the instruction following it.