delp%udel-eecis1.udeecis@udel-ee@sri-unix.UUCP (08/31/83)
From: Gary Delp <delp%udel-eecis1.udeecis@udel-ee> The only time we have run into Parity Check 2 have been when two sets of software/hardware have both tried to use the same DMA channel. -Gary Delp <delp at udel>
jim@rand-unix@sri-unix.UUCP (09/02/83)
I was told that Parity Check 1 refers to an unspecified problem on the motherboard (usually bad memory), and Parity Check 2 is any unspecified problem on an add-on card. I got it a few times on very hot days, but it went away by evening. I suggest using the diagnostics for your add-on cards.
John.Zsarnay@CMU-CS-VLSI@sri-unix.UUCP (09/07/83)
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
john@ecsvax.UUCP (09/15/83)
There have recently been some questions and answers in the Info-IBMPC Digests (V2#59 - news item duke.3481; V2#61 - news item duke.3489) about the PARITY CHECK 2 message that IBM PC's display if some problem is detected in the memory check the PC runs when you turn it on. I have been receiving this message to on my PC, which has the old-style motherboard (with 64K RAM) and a TECMAR quad-function board with 256K RAM, but the problem is intermittent. Before the PARITY CHECK 2 message is displayed, however, a code number 201 and a hexadecimal address show up and then disappear. The address is not the same each time, but it is always for memory between 64K and 320K, so I take it I have a couple of marginal chips (I have ordered replacements). In the meantime, however, I can force the machine to behave by making sure the TECMAR board is seated properly and pressing motherboard memory back into its sockets (I had thought this sort of thing died with the Apple II+). Sometimes the memory check will not report any problems, but chkdsk will either make the system hang or display the PARITY CHECK 2 message. Have others had similar experiences with memory expansion boards other than TECMAR? (I had a 192K Memory Technologies board for a while and never had a problem with it.) john hogan n.c.educational computing service Research Triangle Park, NC 27709 (919) 549 0671 (decvax!mcnc!ecsvax!john)