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Amiga computer related discussion => Amiga Hardware Issues and discussion => Topic started by: jltursan on September 23, 2017, 01:40:25 PM
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I'm experimenting with this eeprom as its capacitity is four times the standard and it's pin compatible with the Amiga kickstart socket.
I've started with the most basic operation to test the compatibility, I've dumped the working KS3.1 from my A600 and flashed the MX with it repeated four times (the usual trick if you don't want to deal with pullups and such).
Well, it doesn't works, I'm only getting a red screen. Then I've also tried pulling out from the socket pins 1 & 40 and connecting them to GND, this way the chip must work like the original; but no way, red screen.
Do I need something special to make it work?, any positive experiences with this eeprom?, although seems identical, maybe there're electrical differences :angry:
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Let me guess, you have a chipram expansion?
Make sure address mapping of the 1.5 MB of extram ROM space does not collide with addresses already in use.
https://amigacoding.com/index.php/Amiga_memory_map
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OMG, do you think that the new ROM is being mapped over RAM?, I'm busted then...
My A600 has indeed 2MB chip and a Furia accelerator; so plenty RAM here :-(
I've never thought about this subject, I'll need to check carefully how it's mapping the RAM right now.
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OMG, do you think that the new ROM is being mapped over RAM?, I'm busted then...
My A600 has indeed 2MB chip and a Furia accelerator; so plenty RAM here :-(
I've never thought about this subject, I'll need to check carefully how it's mapping the RAM right now.
It's being mapped into exactly the same space as the original ROM. Unless you've done modification to your motherboard, it can't be mapped anywhere else.
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OMG, do you think that the new ROM is being mapped over RAM?, I'm busted then...
Well, _ROMEN will only become active when the system attempts to read anything in the 512k of ROM space, starting from $F80000 (or $000000 at power on). So just because you have a larger EPROM, it doesn't magically change the address decoder's range and make it stomp over everything else.
So I don't think that's the problem. The red screen indicates that the system is at least starting to read the ROM correctly, and it's obviously failing the checksum test, meaning it isn't reading the entire 512kB of ROM space reliably/correctly for some reason.
A simple check would be to put the EPROM in your favourite programmer, bend A18 and A19 away so they don't contact the socket, and link them both to ground. Tell your EPROM programmer it's a 27C400, then read out the entire device. The 512kB output should compare correctly to the standard Amiga ROM. If that's OK, it means the correct data is available to the Amiga. If it doesn't verify, you've got some programming problem.
You are using a known good ROM image, right? i.e. the ROM dump you did is actually OK.
Another guess - the Amiga permanently holds CE active and _ROMEN simply gates the Output Enable line. There's a slim chance the device might not like this, perhaps it's using the falling edge of CE to do address setup or something silly. Would seem unlikely, but try removing bending the CE pin so it's not contacting the Amiga ROM socket and tie it directly to OE so that CE and OE get activated together with _ROMEN.
As for using a larger than 512kB ROM, that's another subject for a another thread. Get it working as a standard ROM to begin with.
Interesting find by the way, I've not seen this part before. Where'd you source it from?
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You can find these from several eBay sellers, I've sourced mine from this one (the offer is really good):
http://www.ebay.es/itm/5pcs-MX29F1615PC-10-MX29F1615-Flash-EPROM-DIP-42-/391516410121?hash=item5b28325109:g:k94AAOSwARZXlv3H
The only drawback is that they have a low number of writes (about one hundred); but usually, if they're not used as a tests bed, you'll never reach the limit :-)
Btw, you're right, my dump was bad, I found a dozen of bytes wrong. No idea if the original kickstart is weaking or my trusty Wellon has cheated me. Using an already well-know dump I was able to create a 2MB image successfully: Cloning the first 512KB four times and byte swapping the result was enough, no need to pulldown pins.
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Thanks for trying and starting this thread. I started another thread asking about a Winbond chip and apparently no one else has any experience with them. I am just in the "planning stages" as my 500s and 2000 are not yet in my office.