This does not load 2000 into XR1; it is an indirect instruction, and loads the contents of 2000, which is 101, the return address for that call to SIMPL.
2.
There are also jump indirect and load accumulator indirect instructions which use the accumulator contents as the low 8 bits of an address; the high 7 bits of the current PC are preserved.
3.
"' A plethora of instructions "': Because any instruction acting on a single register can be augmented with its indirect " dual " ( including conditional and unconditional jumps, cf the Elgot-Robinson model ), the inclusion of indirect instructions will double the number of single parameter / register instructions ( e . g.
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