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
enabled.

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
DAL0)"

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



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