EXR

EXR is an assembly instruction. The contents of the register specified in the sr field (bits 3-5 of the instruction) is transferred to the instruction register and then executed as an instruction.

If sr contains a memory reference instruction with P-relative addressing, the address will be relative to the value of the P register for the EXR instruction. If sr contains a JPL instruction, the L register will point to the instruction after the EXR instruction.

It is illegal to use EXR  to fetch another EXR  instruction. Attempting this will set the error flag Z in the status register.