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> SETUSR Set User Mode Rabbit 3000A/4000 Instruction

> Opcode | Instruction | Clocks | Operation
> ED 6F | SETUSR | 4 (2,2) | SU={SU[5:0],0x01}

> 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.

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