prime
Experienced Member
Hi All,
I bought a couple of V20 CPUs recently to upgrade amongst other things my PC-RETRO board and have run across a strange problem with a self designed memory card.
After I fitted the V20 to the PC-RETRO board I found that the machine would POST and boot without problem but at random points after bootup would lockup, produce spurious characters on the screen etc.
Removing my self built RAM card cured the problem, but left me with only 256K, and no UMBs. So I tried replacing the RAM card with a commercial one that I just happened to have in my box of spares (DFI MEMO-576), this worked correctly.
So then I tried my RAM board in another XT class board EXCEL-TURBO, also with a V20 and it WORKED ! no flakeyness or anything.
I'm now stumped as to what the problem is, my RAM card is the one pictured here : https://www.facebook.com/photo.php?fbid=4509299242810&set=a.4468245456491.2168626.1000448675&type=3&theater It's a pretty simple affair, 2 512Kx8 SRAM chips and a CPLD to decode / select addresses to activate the chips.
It should also be noted that the PC-RETRO board works absolutely correctly with the 8088 that was supplied and doesn't have any problems with my board.
Is there a dos based (or bootdisk based) program that I can use to test the memory to see if I can work out what is going on !
Cheers.
Phill.
I bought a couple of V20 CPUs recently to upgrade amongst other things my PC-RETRO board and have run across a strange problem with a self designed memory card.
After I fitted the V20 to the PC-RETRO board I found that the machine would POST and boot without problem but at random points after bootup would lockup, produce spurious characters on the screen etc.
Removing my self built RAM card cured the problem, but left me with only 256K, and no UMBs. So I tried replacing the RAM card with a commercial one that I just happened to have in my box of spares (DFI MEMO-576), this worked correctly.
So then I tried my RAM board in another XT class board EXCEL-TURBO, also with a V20 and it WORKED ! no flakeyness or anything.
I'm now stumped as to what the problem is, my RAM card is the one pictured here : https://www.facebook.com/photo.php?fbid=4509299242810&set=a.4468245456491.2168626.1000448675&type=3&theater It's a pretty simple affair, 2 512Kx8 SRAM chips and a CPLD to decode / select addresses to activate the chips.
It should also be noted that the PC-RETRO board works absolutely correctly with the 8088 that was supplied and doesn't have any problems with my board.
Is there a dos based (or bootdisk based) program that I can use to test the memory to see if I can work out what is going on !
Cheers.
Phill.
the CPLD has a VCC of 3.3V but is 5.0V compatible on it's inputs & outputs, since the only outputs are the /CS lines for the RAMS, which are active low, this shouldn't matter.