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## Known differences between SimH, 11/70, and w11a
### SimH: `SPL` doesn't have 11/70 behavior
On an 11/70, the `SPL` instruction in the 11/70 always fetches the next
instruction regardless of current mode, pending device, or even console
interrupts. This behavior is used in some xxdp diagnostic codes to prepare
a situation suitable for interrupt response testing.
SimH does not implement this behavior, `SPL` behaves like all other
instructions, and interrupts or traps are honored after it completes.
xxdp `ekbbf0` test 32 depends on the 11/70 behavior and is skipped.
The w11 implements 11/70 behavior for `SPL` in kernel mode only. In supervisor
or user mode `SPL` is a nop and honors traps and interrupts, see
[`SPL` on w11](w11a_diff_70_spl_bug.md).