NobodyIsHere
Veteran Member
- Joined
- Dec 21, 2006
- Messages
- 2,410
Hi
So I am finally getting around to building one of these XT-IDE V2 PCBs. I found one issue that sort of bugs me though.
I built the board using the schematic, PCB layout, the wiki, etc. Everything seemed to go well and no release of magic smoke.
However I noticed some data corruption on boot with my IDE hard drive. The hard drive worked just fine with the XT-IDE V1 boards (both of them).
Even the prototype boards work fine with the drive so I am sort of puzzled.
I am using an old but working XT-IDE ROM (v 0.10) and configured both the XT-IDE V2 and XT-IDE V1 in nearly identical form except for the location of the ROM. However moving the ROM around in memory did not have any obvious effect AFAIK.
Pulling out my few remaining gray hairs, I trying to figure out what is the problem. I do all the obvious stuff like reheat all the solder joints, check all the chips in the tester, ring out the circuit against the schematic, etc. Still occasional corruption with no obvious reason.
By pulling every chip except those absolutely required I was able to isolate the problem to the actual IDE drive latching circuitry. The ROM seems to work fine no matter what. The UART circuitry is gone so I dig into the IDE circuitry more closely.
Everything in the IDE circuitry seems to check out. I am stumped so I resort to chip swapping to further isolate the problem.
Then I noticed that I used 74ALS245 bus transceiver rather than the recommended 74LS245. My XT-IDE V1 boards use the 74F245 transceivers and they work great. Swap out the 74ALS245 for either a 74F245 or a 74LS245 and the XT-IDE V2 board work great just like the XT-IDE V1s and the prototype boards.
WTF! Happy day! I found the problem! Yay! Not so happy is why this *is* a problem. I swap out the 74ALS245s for other 74ALS245s and they all have the same bad behavior. All the 74ASL245s check out on the chip tester.
I guess I was thinking or just assumed that 74ALSxxx was basically interchangeable for 74LSxxx. ALS is Advanced Low Power Schottky and I thought was just LS only better in every conceivable way. Well, with one little exception... IT DOESN'T WORK!
Ideas? I realize the 74ALS245 is a significantly faster part than the 74LS245 but then so is the 74F245 and it works fine. I am surprised and bit disturbed this is making any noticeable difference.
Take it for what it's worth. Obviously there is a fairly significant difference. I am going to dig into the datasheets and see if I can figure out what is the issue. Intuitively, I think 74LS parts would be more compatible with the IBM PC I am using. Nearly everything else in the test unit is 74LS or similar technology. Also it is a fairly slow and gentle machine at only 4.77 MHz
Thanks and have a nice day!
Andrew Lynch
So I am finally getting around to building one of these XT-IDE V2 PCBs. I found one issue that sort of bugs me though.
I built the board using the schematic, PCB layout, the wiki, etc. Everything seemed to go well and no release of magic smoke.
However I noticed some data corruption on boot with my IDE hard drive. The hard drive worked just fine with the XT-IDE V1 boards (both of them).
Even the prototype boards work fine with the drive so I am sort of puzzled.
I am using an old but working XT-IDE ROM (v 0.10) and configured both the XT-IDE V2 and XT-IDE V1 in nearly identical form except for the location of the ROM. However moving the ROM around in memory did not have any obvious effect AFAIK.
Pulling out my few remaining gray hairs, I trying to figure out what is the problem. I do all the obvious stuff like reheat all the solder joints, check all the chips in the tester, ring out the circuit against the schematic, etc. Still occasional corruption with no obvious reason.
By pulling every chip except those absolutely required I was able to isolate the problem to the actual IDE drive latching circuitry. The ROM seems to work fine no matter what. The UART circuitry is gone so I dig into the IDE circuitry more closely.
Everything in the IDE circuitry seems to check out. I am stumped so I resort to chip swapping to further isolate the problem.
Then I noticed that I used 74ALS245 bus transceiver rather than the recommended 74LS245. My XT-IDE V1 boards use the 74F245 transceivers and they work great. Swap out the 74ALS245 for either a 74F245 or a 74LS245 and the XT-IDE V2 board work great just like the XT-IDE V1s and the prototype boards.
WTF! Happy day! I found the problem! Yay! Not so happy is why this *is* a problem. I swap out the 74ALS245s for other 74ALS245s and they all have the same bad behavior. All the 74ASL245s check out on the chip tester.
I guess I was thinking or just assumed that 74ALSxxx was basically interchangeable for 74LSxxx. ALS is Advanced Low Power Schottky and I thought was just LS only better in every conceivable way. Well, with one little exception... IT DOESN'T WORK!
Ideas? I realize the 74ALS245 is a significantly faster part than the 74LS245 but then so is the 74F245 and it works fine. I am surprised and bit disturbed this is making any noticeable difference.
Take it for what it's worth. Obviously there is a fairly significant difference. I am going to dig into the datasheets and see if I can figure out what is the issue. Intuitively, I think 74LS parts would be more compatible with the IBM PC I am using. Nearly everything else in the test unit is 74LS or similar technology. Also it is a fairly slow and gentle machine at only 4.77 MHz
Thanks and have a nice day!
Andrew Lynch