On Sep 9, 2016, at 6:11 PM, Noel Chiappa <[email protected]> wrote: > >> If your CPU is an 11/73 (which can directly 'access' [hate that verbism >> :-] all of memory from ODT, unlike the 11/23 which is restricted to the >> bottom 256KB), try playing around with a failing location, and its >> alternative, directly, and see if a store of random data into one can be >> read back directly from the other > > Note: The 11/'73' CPU powers up with the cache enabled, even for ODT! > > So if you write xxx into some location, if you then read it back, you will get > the correct data even if the memory location is busted - the CPU is getting > the (correct) data from the cache. To have your 'memory' reads and writes > actually go to the memory, you need to turn off the cache: > > 17777746/ 02000 > > Note that starting the machine does an INIT, which will again enable the > cache. >
That’s a very good piece of information, I hadn’t considered that. I have 11/73. I’ve checked the memory with ODT and can confirm the stuck bit. I found that EK-MSV1Q-UG-002_MSV11Q_5-85.pdf describes how the CVMSAA diagnostic works. "Section 1: Address Tests These tests verify the uniqueness of every memory address.Test 1 writes and reads the value of each memory word address into that memory location. After all memory has been written, all locations are checked again. “ I interpret this as mean it will deposit 1000 into @1000, and that will be read back as 1400 given the bad bit. So if you have stuck bit, the test for uniqueness gives a false positive. A comic ray probably took out a logic gate, as there is a pattern of stuck 1 bits in the chip. As soon as I pick up a spare chip, I start to get invasive. A careful clipped VCC is easily restored if its the wrong chip. Jerry
