Q22 BUS parity check?

9000 VAX vax9000 at gmail.com
Tue Dec 12 22:29:51 CST 2006

OK, I did some experiment and found the answer. See below.

On 12/12/06, 9000 VAX <vax9000 at gmail.com> wrote:
> Hello,
>   I read the Q22 specification (search "Q22 specification" on this page:
> http://www.chd.dyndns.org/qbus_ide/ ) but the parity check function is
> still not clear to me. My questions are,
> 1. Is there parity check when interrupt vector is read ?

Not tested. My guess is no.

2. Is there parity check if IO page is read?

It is either no parity for I/O page, or my implementation is wrong.
I get machine check error when "show dev", if I/O page parity on my board is

3. What is the polarity of the parity bit?

(background: Q22 BUS uses negative logic. A "low" measured on the slots
means '1'.) The parity bit is computed as "not (DAL15 xor DAL14 xor ... xor

Those questions are not answered from the specification. Any expert here?
> Thanks
> vax, 9000

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