A500 won't work with official (MX) 2.04 ROM

r.cade · 04 October 2021, 14:12

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.

jbenam · 04 October 2021, 14:30

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?

r.cade · 04 October 2021, 14:41

Quote:

Originally Posted by jbenam

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?

No, it works in the other A500. I didn't realize these were EPROMs. This A500 may need the pullup resistors?

Besides, I figured an A600 ROM would work if it was...

jbenam · 04 October 2021, 14:56

Quote:

Originally Posted by r.cade

No, it works in the other A500. I didn't realize these were EPROMs. This A500 may need the pullup resistors?

Besides, I figured an A600 ROM would work if it was...

Now that I think of it, they might be mask ROMs. Which is probably the case. So yes, my bad, they are Mask ROMs.

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.

TroyWilkins · 04 October 2021, 15:14

Quote:

Originally Posted by jbenam

Now that I think of it, they might be mask ROMs. Which is probably the case. So yes, my bad, they are Mask ROMs.

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.

I did this, back in the day, to see if it would work. I put a Kickstart 2 ROM (not sure now if it was 37.299, 37.300 or even 37.350) from an A600 into an A500, and the Kickstart 1.3 (again, not sure exactly which version it was) into the 600. The 600 didn't have a 2.5" HDD in it, so losing access to that didn't matter, and both machines worked perfectly well with the 'wrong' ROM in them.

jbenam · 04 October 2021, 15:49

Quote:

Originally Posted by TroyWilkins

I did this, back in the day, to see if it would work. I put a Kickstart 2 ROM (not sure now if it was 37.299, 37.300 or even 37.350) from an A600 into an A500, and the Kickstart 1.3 (again, not sure exactly which version it was) into the 600. The 600 didn't have a 2.5" HDD in it, so losing access to that didn't matter, and both machines worked perfectly well with the 'wrong' ROM in them.

Nice, thanks for sharing your experience. Good to know

r.cade · 13 November 2021, 00:30

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.

jbenam · 13 November 2021, 08:59

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

Overdoc · 14 November 2021, 23:05

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?

Jope · 15 November 2021, 08:43

Rev 5 + 1.3 is quite common based on the machines I've seen. Only the earliest rev 5 machines came with 1.2 :-)

04 October 2021, 14:12	#1
r.cade Registered User Join Date: Aug 2006 Location: Augusta, Georgia, USA Posts: 550	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.

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04 October 2021, 14:30	#2
jbenam Italian Amiga Zealot Join Date: Jan 2009 Location: Italy Age: 36 Posts: 1,910	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?

13 November 2021, 00:30	#7
r.cade Registered User Join Date: Aug 2006 Location: Augusta, Georgia, USA Posts: 550	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
jbenam Italian Amiga Zealot Join Date: Jan 2009 Location: Italy Age: 36 Posts: 1,910	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
Overdoc Commodore Collector Join Date: Aug 2001 Location: Austria Age: 53 Posts: 944	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
Jope - Join Date: Jul 2003 Location: Helsinki / Finland Age: 43 Posts: 9,861	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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