Is it possible to build a breadboard device to simply view the code burned into a 28 pin or 40 pin DIP chip? I do not intend to do any erasing/programming on the chips, just wanted to view what is on them without the expense of a full-blown EPROM programmer device.
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3There are several ways. One such way is to use an Arduino. Check out this link: github.com/sanni/cartreader The practice should be similar to different EPROM's.– cbmeeksSep 5, 2017 at 20:26
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4 Answers
Jup, extreme simple, as EPROMs are static devices. Just connect a bunch of switches to the adress lines and some LED (use modern low power and don't forget the resistors) to the data lines, pull CS and OE and look whats on each address. You may even spare the switches and setup the address just with wires :)) I hope this isn't too low level.
Another way would be using that EPROM in some old computer. For a 2716 I'd pull out an Apple II and plug it into some extension card with an according socket (or instead of BASIC :)) and use the monitor to browse the content. YMMV.
While you can use toggle switches to enter addresses as @Raffzahn suggests (and it has a bit of the true retro authenticity to it: you'll be doing exactly the same operation that users of computers like the MITS Altair were doing to make them work), it's a lot of working.
The 74LS393 is a relatively cheap chip that contains a pair of 4-bit counters. They count on negative edge of a clock signal, so if you connect the high-order bit of one to the clock input of the other, it becomes an 8-bit counter: pulse the clock repeatedly and it'll count up to 255 then switch back to 0. Connect two of those together in the same fashion and you get a 16-bit counter. Hook this up to the address lines of your eprom and then you can just press a button to get the next value, rather than having to make a complex sequence of adjustments by hand every time.
Here's a page where somebody has implemented a similar device (in this case capturing the output of the EPROM into an Arduino so that it can be stored for later reprogramming) along with a diagram showing how to cascade the counters as I describe above.
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:)) I wouldn't call it a complex sequence, as 27xx EPROMs are static operated. Thus adjusting the adress is all it needs. Then again it depends on what parts are available in your hack cave.– RaffzahnSep 5, 2017 at 22:59
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3@Raffzahn - I say complex because you'll need to change more than one switch between each typical address. It becomes very annoying after the first few hundred bytes...– JulesSep 6, 2017 at 0:14
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@Jules not if you step through the addresses using Gray Code, and then write some (trivial) modern software to sort the results back into address order. See en.wikipedia.org/wiki/Gray_code. Sep 6, 2017 at 0:58
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Thank you for the suggestions, I will try to make it work. I need a hack cave lol. Sep 6, 2017 at 2:02
To add a price point, the Minipro TL866CS is under $50 and lets you read and write EPROMs. Check the compatibility list to see if your chip is natively supported. I needed to write 27C400 chips which are not supported so I assembled an adapter board for it which works perfectly.
answered Sep 6, 2017 at 4:00
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Thank you, Traal. Here is (hopefully not off topic) a related question. The data sheet for a 28-pin Toshiba chip I have is this: alldatasheet.com/datasheet-pdf/pdf/31704/TOSHIBA/… Would this memory chip have code in it if I were to view it on the device, or using the other ideas in this post? Sep 6, 2017 at 18:46
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2@BobRutledge According to the datasheet, that chip is an SRAM. So it is not quite as volatile (no refresh needed) as DRAM but it will lose memory once you remove power. The datasheet says it is pin-compatible with an EPROM, so for system design that can be a plus - but this chip is not an EPROM itself. Sep 6, 2017 at 18:54
Half OT, but whatever: Once you built this breadboard circuit, try to get your hand on some 2816/2864/... chips (not 28Fxxx flash!) - these EEPROMs share a pinout with the 27xx EPROMs and are easy enough to write to(!) that it can be done in a breadboard setup too.
