04 October 2021, 14:12 | #1 |
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A500 won't work with official (MX) 2.04 ROM
I have a couple of A500's- both are Rev.5 boards.
One works fine with 1.3 kickstart ROM that it came with, but will not work with an official 2.04 ROM. I have a few, two say "MX" on them and one doesn't but they are not EPROMs. The other works with all the ROMs. The wire link between 1-31 doesn't matter- it just get a black screen and sometimes colorful flashing, just like if there is no ROM installed. Is there some other difference in the boards that could cause this? It works perfectly fine with the 1.3 ROM. |
04 October 2021, 14:30 | #2 |
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MX is just the brand the EPROM uses. They are still EPROMs (not EEPROM, though), they are just OTP (one-time programming) variants. It stands for Macronix (these days you can also see MXIC).
Are you sure it's an A500 2.04 ROM? Maybe it's for an A600? |
04 October 2021, 14:41 | #3 | |
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Besides, I figured an A600 ROM would work if it was... |
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04 October 2021, 14:56 | #4 | |
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While I have heard of A500 ROMs working fine on an A600 (with features lacking, obviously), I have never tried to do the opposite, so I wasn't sure if it would just work. Anyway, Commodore had a lot of variance even between the same revision of the boards. Are you sure the boards look exactly the same? One might be lacking some resistors, for example. |
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04 October 2021, 15:14 | #5 | |
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04 October 2021, 15:49 | #6 | |
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13 November 2021, 00:30 | #7 |
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This particular A500 (Rev.5) has a problem where it won't work even with an original Kickstart 1.2 ROM.
I built the adapter board with the 4.7k resistors that is supposed to fix the issue with EPROMs on A500, and now the original 1.2 ROM works, and the 2.04 ROMs also all work fine. Bizarre... It only works natively with the 1.3 ROM that came with it. That 1.3 masked ROM looks identical to the 1.2 ROM, other than the 1.2 is part number -01 instead of -02 on the 1.3. |
13 November 2021, 08:59 | #8 |
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Even if they have the same number of pins, they might work differently. Sadly the Commodore part number doesn't tell the entire story, we should know what kind of Masked ROM they used in the first place to compare the pinouts on the datasheets and see if there are any differences.
Probably this production run had some issue and Commodore decided it would be quicker to use a slightly different mask ROM instead of fixing the board itself. Anyway, glad you fixed it |
14 November 2021, 23:05 | #9 |
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It is interesting that this rev. 5 board already came with a kick 1.3.
So it must be one of tha latest rev. 5 boards, before they did rev. 6 (which I think only came with kick. 1.3?) Maybe they did some minor changes on those latest rev.5 boards? |
15 November 2021, 08:43 | #10 |
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Rev 5 + 1.3 is quite common based on the machines I've seen. Only the earliest rev 5 machines came with 1.2 :-)
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