On 05/11/2007 21:17, Gordon JC Pearce wrote: If it's really a stuck bit regardless of address (within the bank), a logic probe might show you, though you might need to make up a really sophisticated circuit with an LS TTL OR gate to only show you the data when the chip select line for the bank you're testing is low. Or use a 'scope and set it to only trigger on the appropriate chip select. I've got a fast Z80 memory test routine I once wrote for a project, which tests every bit for address, stuck-at, coupling, and some pattern faults, which runs from ROM. It tests 8K bytes on a 4MHz Z80 in about 6 seconds unless it finds faults (and then writing the information to the display slows it down). It doesn't need any RAM at all, though it was written to drive a 2-line 16-char LCD display mapped to an address in the target system. You could probably modify it to write to whatever you can use in -- or hung off -- the Superbrain. Give me a shout if you want a source listing. -- Pete Peter Turnbull Network Manager University of York