Knut wrote:
"Michael J. Mahon" wrote:Linards Ticmanis wrote:Knut Roll-Lund wrote:Grasping at straws: What if there is an adressing problem that data is overwritten because of an adress line failure. Would APTEST see that? Is there a RAM test that would test the address lines?I don't think APTEST would see this at all. The RAM test in APTEST is extremely simple minded: fill all of RAM with Value X, then test if it's still there. Repeat for next X. This obviously won't find broken or flaky address lines. You could try something simple like this (with no DOS loaded): 10 FOR I = 2500 TO 49000 STEP 2 20 PRINT I; 30 POKE I, 85:POKE I+1, 170 40 NEXT I 50 FOR I = 2500 to 49000 STEP 2 60 PRINT I; 70 POKE I, 170:POKE I+1, 85 80 NEXT I Then see if and at what value of I you get screen corruption.Or you could take two passes, and store the high/low byte of the address at each address, then read back and verify. If any address line is open, stuck, or shorted to another, the values read back will not match.Hi, thanks for the answers.I have designed simple RAM tests through my work (embedded stuff). I would typically test address lines by using powers of two for each RAM area (in assembly using registers so the RAM is free) writing and reading back to see if they would affect each other.I'm still learning about the Apple2 and especially I don't yet know where it is allowed to POKE. I could probably interpolate on your program and use the area 2500 to 49000 to test all the address lines, test separately within each bank of RAM.BTW I did have a flaky RAM, at first, but identified it and fortunately I have some compatible spares. It sometimes got through the APTEST and sometimes not. I have been moving the RAM chips around so I'm pretty sure they work now (tested them all in the first bank). The faulty RAM was originally in the middle bank so DOS3.3 would boot fine even with it failing.
Marginal DRAM is usually forced into failure by high temperatures, so you could direct a heat lamp or hair dryer at the DRAM (selectively, even) while testing to weed out any marginal chip(s). -michael NadaNet file server for Apple II computers! Home page: http://members.aol.com/MJMahon/ "The wastebasket is our most important design tool--and it's seriously underused."