GandALF, substitute for the MOS 325572-01

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eslapion
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GandALF, substitute for the MOS 325572-01

Postby eslapion » Fri Jul 21, 2017 11:11 pm

I was about to post this in the 'Other Systems' section... wrong! The 1541 is a peripheral used on the VIC-20 before any other systems.

It is with great pride that I announce you all that in the coming weeks, I will be offering a new product.

GandALF is a replacement module for the MOS 325572-01 custom IC installed in all VIC-1541 and 1541 disk drives that use the mid sized boards (1540050, 250442 and 250446).

The Gate and Array Logic for Floppy is about the only component on the electronics board of the standard 1541 and the later VIC-1541 for which there is no current version or cross reference on modern components list.

Using technology similar to what's used on PLAnkton, me, e5frog (Fredric Blaholtz) and electrical engineer Sylvain Brisebois were able to create a fully functional and perfectly compatible module to replace this IC which is specific to the 1541 series of floppy disk drives and only ever made by MOS or the Commodore Semiconductor Group.

No other company or individual has ever previously offered a compatible or equivalent replacement component.

More details will follow. Please feel free to ask any sales related and technical questions.
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Re: GandALF, substitute for the MOS 325572-01

Postby norm8332 » Sat Jul 22, 2017 7:34 pm

Sounds cool, I'm glad its being made. Is this a chip that fails often? I have encountered 11 non-functioning 1541s (I know not many) and only two were non repairable due to bad heads...I never encountered a bad one of these. With that said, I think it's great that you are making them and helping keep the drive alive. Thanks.

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Re: GandALF, substitute for the MOS 325572-01

Postby eslapion » Sat Jul 22, 2017 11:44 pm

norm8332 wrote:Sounds cool, I'm glad its being made. Is this a chip that fails often? I have encountered 11 non-functioning 1541s (I know not many) and only two were non repairable due to bad heads...I never encountered a bad one of these. With that said, I think it's great that you are making them and helping keep the drive alive. Thanks.

It's not a chip that fails often but everything else on the board (sorry, the RW head is not on the board...) is either still being made or easily substituted.

This specific chip was exclusive to Commodore and nobody made any substitute.

This was not done with the idea that I would sell a lot of them but rather with documenting this chip and understanding what goes on at the lower level of the 1541. AFAIK, even the 1541 Ultimate does not go that far because it emulates a 1541 at the GCR level, not the track bits level.
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Re: GandALF, substitute for the MOS 325572-01

Postby groepaz » Sun Jul 23, 2017 6:27 am

This was not done with the idea that I would sell a lot of them but rather with documenting this chip and understanding what goes on at the lower level of the 1541.

so where is said documentation? :)

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Re: GandALF, substitute for the MOS 325572-01

Postby RobertBe » Sun Jul 23, 2017 7:49 am

Interesting development. Interesting name! :)

Does it use less power? (What is its current draw?) Does it run cooler?

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Re: GandALF, substitute for the MOS 325572-01

Postby eslapion » Sun Jul 23, 2017 11:38 am

RobertBe wrote:Does it use less power? (What is its current draw?) Does it run cooler?

Not in this particular case. The genuine MOS 325572-01 uses very little power and doesn't dissipate much heat at all but it can get damaged when one of the 6522 of the 1541 drive malfunctions.
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Re: GandALF, substitute for the MOS 325572-01

Postby RobertBe » Sun Jul 23, 2017 2:58 pm

eslapion wrote:The genuine MOS 325572-01... can get damaged when one of the 6522 of the 1541 drive malfunctions.

If the 6522 fails, will the GandALF get damaged, or is it more robust?

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Re: GandALF, substitute for the MOS 325572-01

Postby eslapion » Sun Jul 23, 2017 3:49 pm

RobertBe wrote:If the 6522 fails, will the GandALF get damaged, or is it more robust?

Yes because if there is a short circuit on its outputs, the current from it's built-in power supply is limited and so the voltage will collapse but the biggest difference between GandALF and the genuine MOS 325572-01 is somebody is making more of them.
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Re: GandALF, substitute for the MOS 325572-01

Postby cbmeeks » Tue Jul 25, 2017 6:41 am

I think this is a great idea. And I LOVE the name. :-)

Now, if someone would do a drop-in replacement for the VIC-II (and VIC-I) that would be awesome. Something along the lines of what the F18a (TMS9918) did for Coleco, MSX, etc.
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Re: GandALF, substitute for the MOS 325572-01

Postby eslapion » Tue Jul 25, 2017 9:29 pm

cbmeeks wrote:I think this is a great idea. And I LOVE the name. :-)

Thanks for the vote of confidence. This encourages me to push further.

Now, if someone would do a drop-in replacement for the VIC-II (and VIC-I) that would be awesome. Something along the lines of what the F18a (TMS9918) did for Coleco, MSX, etc.

Creating replicas of the VIC-I or VIC-II is incredibly difficult. These chip's internal structure is very poorly documented and in the case of the VIC-I, I can only raise my hat off to lance.ewing for the job he has done so far in this area.

GandALF operates with about 50 macrocells. A 6526 would require more than 200 macrocells, I suspect even more would be required for the VIC-I and more than double again for the VIC-II.
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Re: GandALF, substitute for the MOS 325572-01

Postby cbmeeks » Wed Jul 26, 2017 6:19 am

eslapion wrote:Creating replicas of the VIC-I or VIC-II is incredibly difficult. These chip's internal structure is very poorly documented and in the case of the VIC-I, I can only raise my hat off to lance.ewing for the job he has done so far in this area.


I completely agree. Same goes for the SID. We have some emulation options for the SID but it's just that...emulation.

That would be about all we could do for creating a drop-in replacement for the VIC chips...emulate it as best we can with an FPGA of decent size. Still, I'm surprised it hasn't been done. I know there are plenty of C64 cores out there but no drop-in replacement boards that I'm aware of.
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Re: GandALF, substitute for the MOS 325572-01

Postby groepaz » Wed Jul 26, 2017 6:26 am

drop-in replacement havent been done because a) they are even harder to do than a complete FPGA core (you must meet external timing at all times) and b) they would be quite expensive (likely more expensive than real chips)

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Re: GandALF, substitute for the MOS 325572-01

Postby eslapion » Fri Jul 28, 2017 6:08 am

cbmeeks wrote:That would be about all we could do for creating a drop-in replacement for the VIC chips...emulate it as best we can with an FPGA of decent size. Still, I'm surprised it hasn't been done. I know there are plenty of C64 cores out there but no drop-in replacement boards that I'm aware of.

I'm not surprised at all. Making a core requires only good programming knowledge and abilities. Making a drop-in sub requires thorough EE knowledge and understanding.

The VIC-I and VIC-II are a really special case because they incorporate both digital and analog electronics technology.

I suppose it was possible to make drop-in subs for the SID because the pace at which it generates signals is so much lower than a video chip so programming on a very fast microcontroller was enough to compensate for a lack of EE knowledge. You can't get away with this with a video chip.
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Re: GandALF, substitute for the MOS 325572-01

Postby groepaz » Fri Jul 28, 2017 8:01 am

The VIC-I and VIC-II are a really special case because they incorporate both digital and analog electronics technology.

there is very little analog stuff in either. if you make the replacement generate for example HDMI instead of analog video, then you can eliminate all of that. (and even if you dont, using a sigma-delta DAC instead of the analog voltage divisor is not rocket science either)

the SID btw generates output at 1Mhz - and contains a whole lot more analog stuff than any other chips in a CBM machine.

and no, lack of EE knowledge certainly is not a reason for it :)

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Re: GandALF, substitute for the MOS 325572-01

Postby cbmeeks » Fri Jul 28, 2017 8:23 am

eslapion wrote:I suppose it was possible to make drop-in subs for the SID because the pace at which it generates signals is so much lower than a video chip so programming on a very fast microcontroller was enough to compensate for a lack of EE knowledge. You can't get away with this with a video chip.


Yeah, I'm not sure I agree with that. The F18a (a TMS9918 drop-in replacement) was designed by someone learning EE. And, over time, it became a 100% cycle-accurate replacement that uses VGA instead of composite. I have one in one of my TI's and it works wonderfully.

Yes, I realize the TMS9918 isn't quite the chip the VIC-II is but I would say it's on-par with the VIC-I. Plus, the designer added new features like better scrolling, better sprite support and more colors. I admit, however, that the TMS9918 is very well documented (+1 for TI).

But the reason I'm surprised a replacement VIC-II hasn't been done (drop-in replacement) is because of the popularity of the C64 is so great. Having a VGA and/or HDMI replacement board would be awesome. It wouldn't be perfect...I get that. But over time, it would get closer and closer and eventually, be "good enough" for *most* people.

I wished I had the EE chops to do it myself.

Maybe we should all plead with the designer of the F18a to do a VIC-I replacement for our VIC-20's! Something to provide VGA support at least. I bet he has the skills to do it now.
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