[Simh] Problem with MT_ASTLVL on the VAX-11/780

[Jeremy Begg]

Hi Johny,

> Hum. Do I remember wrong? I seem to remember that when you MOVB to a register, the value should be sign extended. So not just the low byte should have been modified.

I thought so too, but decided to check and found this is not true.

From the “VAX Architecture Handbook”, 1981, page 179:

“Unlike the PDP-11, but like the other VAX-11 instructions, MOVB and MOVW do not modify the high order bytes of a register destination.  Refer to the MOVZxL and CVTxL instructions to update the full register contents.”

Regards,

        Jeremy Begg

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