Hi everyone!
Recently, I've been trying to bring an old computer back to life. Because of it's age, I'm worried if the EPROMs (two) that store the OS and interpreter still have it's data in original state. The ICs are about 23 years old, and one lost the quartz window protecting stick 10 years ago. It hasn't been exposed to strong sunlight or any light at all, but it may be compromised.
The ICs are HN482764G = 2764. Since I don't have an EPROM Reader/Programmer, I implemented a reading device using an AVR.
I just did some hacking on my breadboard, so I did a quick sketch of the schematics to attach here. As you can see, what I've done is wire my EPROM to AVR ports and carefully handle the communication by toggling it's control lines and clocking the 4040 to drive the address lines.
The AVR I'm using is a AT90USB162, mounted on a mini dev-board. The one on schematics isn't the correct part, as KiCAD doesn't have it. But it's the same thing concept-wise.
It's seems I've succedded to some extent. I can sample my AVR ports that are wired to the output pins of the EPROM and get the data back (and then send by USB, as a CDC serial device to my PC).
The problem is that my readings aren't reliable. If I try to read the same address over and over, I get two (sometimes three) different values.
I thought it would be a timing problem, but I tried increasing the delay between various steps in the communication (like the delay to gate data out after pulling G (output enable) low). I even tried something like 1 ms, that's way longer (and more safe) than the specified in datasheet (in nanoseconds). No success.
Does anyone have an comment or suggestion on what's going on? Mostly a timing problem? I've been wondering if I need to pull-up the data lines.
Maybe my EPROMs are so old that the data is trashed. Or the ICs are faulty. I've tried with both EPROMs and they have the same behaviour.
Or even worse: maybe I'm completely off with my schematic/code/ideas!
If anyone have some words to share about it, I would be very grateful! If more information is needed (like the AVR code), please tell me, I'll promptly reply!
Thank you very much for your time.
Best regards.
Recently, I've been trying to bring an old computer back to life. Because of it's age, I'm worried if the EPROMs (two) that store the OS and interpreter still have it's data in original state. The ICs are about 23 years old, and one lost the quartz window protecting stick 10 years ago. It hasn't been exposed to strong sunlight or any light at all, but it may be compromised.
The ICs are HN482764G = 2764. Since I don't have an EPROM Reader/Programmer, I implemented a reading device using an AVR.
I just did some hacking on my breadboard, so I did a quick sketch of the schematics to attach here. As you can see, what I've done is wire my EPROM to AVR ports and carefully handle the communication by toggling it's control lines and clocking the 4040 to drive the address lines.
The AVR I'm using is a AT90USB162, mounted on a mini dev-board. The one on schematics isn't the correct part, as KiCAD doesn't have it. But it's the same thing concept-wise.
It's seems I've succedded to some extent. I can sample my AVR ports that are wired to the output pins of the EPROM and get the data back (and then send by USB, as a CDC serial device to my PC).
The problem is that my readings aren't reliable. If I try to read the same address over and over, I get two (sometimes three) different values.
I thought it would be a timing problem, but I tried increasing the delay between various steps in the communication (like the delay to gate data out after pulling G (output enable) low). I even tried something like 1 ms, that's way longer (and more safe) than the specified in datasheet (in nanoseconds). No success.
Does anyone have an comment or suggestion on what's going on? Mostly a timing problem? I've been wondering if I need to pull-up the data lines.
Maybe my EPROMs are so old that the data is trashed. Or the ICs are faulty. I've tried with both EPROMs and they have the same behaviour.
Or even worse: maybe I'm completely off with my schematic/code/ideas!
If anyone have some words to share about it, I would be very grateful! If more information is needed (like the AVR code), please tell me, I'll promptly reply!
Thank you very much for your time.
Best regards.
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