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Path: utzoo!linus!philabs!seismo!hao!hplabs!sri-unix!John.Zsarnay@CMU-CS-VLSI
From: John.Zsarnay@CMU-CS-VLSI@sri-unix.UUCP
Newsgroups: net.micro.pc
Subject: Re: Parity Check 2
Message-ID: <4841@sri-arpa.UUCP>
Date: Wed, 7-Sep-83 02:06:51 EDT
Article-I.D.: sri-arpa.4841
Posted: Wed Sep  7 02:06:51 1983
Date-Received: Mon, 5-Sep-83 22:12:20 EDT
Lines: 23

The "Parity Check 2" means that a parity error occurred on the I/O channel
(i.e. expansion bus).  A parity error on the system board will cause
a "Parity Check 1" error.

You are probably accessing uninitialized RAM on the expansion boards,
in which case the data could very well have incorrect parity.
The system startup contained in the BIOS ROMs initializes and tests
system memory before booting from disk (or running ROM Basic).  However, if
you have any memory above that configured by the switches on the system
board, it will not be initialized.  The software using the extended memory
should do the initialization itself.

If that isn't your problem, you may have a problem in the I/O channel parity
circuit on your system board.  Parity can be disabled by setting some
control register bit.  I don't have my Technical Reference Manual here, so I
can't give you details.

As for the parity check caused by two programs using the same DMA channel:
You probably confused the DMA controller so much that it stopped performing
memory refresh cycles.  Without refresh, the data in RAM will change
and could cause parity errors.

John