From: Bob Supnik <bsupnik@nauticusnet.com>
Newsgroups: alt.sys.pdp10,alt.sys.pdp11,vmsnet.pdp-11
Subject: Outcome: How RH11/RH70 work
Date: Fri, 05 Oct 2001 11:55:20 -0400
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Thanks to Johnny Billquist, Louis Chretien, Tim Litt, John Wilson, and
others, I can now answer the question about RH11/RH70 interrupts.

The RH11/RH70 will latch and interrupt request if:

- IE is set and RDY (DONE) transitions from 0 -> 1
- IE is set, CS is asserted and RDY is also asserted
- IE and RDY are both written as 1's

The RH11/RH70 clear IE as part of an interrupt acknowledge cycle.

Thus, DONE interrupts are edge-sensitive, but CS interrupts are
level-sensitive; CS interrupts only occur if a data transfer is not in
progress (RDY = 1); and there is a special mechanism for software to
trigger interrupts.

/Bob