Q22 BUS parity check?

9000 VAX wrote: Definitely not an expert (and since none have volunteered), I think that the parity check of the Qbus is an indication of a parity error rather than part of a parity check function. The DEC Bus Handbook with a section on the LSI-11 bus says that BDAL17 is parity check enable and BDAL16 is parity check error. http://www.bitsavers.org/pdf/dec/pdp11/handbooks/PDP11_BusHandbook1979.pdf It says that on DATI cycles the bits are controlled by the peripheral. I make the assumption that asserting both during the data transfer phase will indicate a parity error that was detected in the peripheral and asserting only BDAL17 would indicate there was no error (but that parity was checked). It further says that during DATO cycles asserting BDAL16 will write a parity error to memory and BDAL17 is not used on writes. I presume this would be for testing of some kind. -chuck