## Known differences between SimH, 11/70, and w11a

### SimH: traced `WAIT` has J11 behavior

On an 11/70 (and an 11/45) a traced `WAIT` will wait until an interrupt happens
and finish without raising a trace trap because the interrupt has higher
service precedence. The trace trap related to the `WAIT` will happen when the
interrupt driver exits with an `RTI`.
See also [trap and interrupt service order](simh_diff_service-order.md).

On a J11 and other PDP-11 models, a traced `WAIT` falls through and raises a
trace trap immediately. This is consistent with trace traps having higher
precedence in those models.

SimH uses the J11 service order with interrupts having the lowest priority for
all PDP-11 models, and consequently, a traced `WAIT` falls through and raises
a trace trap immediately.
xxdp `ekbbf0` test 63 verifies the 11/70 behavior and is skipped.

The w11 implements the proper 11/70 service order and `WAIT` behavior.