C64 floppy to Atari conversion

[macsonny]

Ok, before everyone loses it over the question, just wondering if it's possible to take the back interface out of a C64 floppy drive and swap it over (somehow) to work with an Atari 130XE?

 

Asking for a friend

[NorbertP]

It depends why you want to do it. If you're hoping it will somehow allow you to read C64 disks on your 130XE then you'll be out of luck. The mechanisms may be compatible, but it's the controller that deals with the actual "how to get data off the disk" business.

[Dinadan67]

I don't think such a conversion would be possible, the 1541 Floppy uses different drive mechanics than Ataris 1050 and is lacking the track-0 sensor.

[Rybags]

Probably.   But then you'd need to design firmware for the 1541 to interface to the drive mech then use SIO to talk to the Atari.

 

A much easier solution would be to just emulate the C64 serial comms from the Atari.  A bit of hardware interface needed but most of the work would be in software.

Unsure if Pokey could do the serial comms - we might be screwed over since you can't turn off start/stop bits.

So the alternative would be to bit-bang.  The stock drive is fairly slow so it would probably work.

 

I was considering once doing the other way around - get a C64 to talk to an Atari drive.  To do raw sector R/W it would be a somewhat easier project.

But in the end, neither one really worthwhile other than to say you did it.  The easiest data interchange would be to just use existing PC based systems.

 

Back in the day, I did a C64 to Atari interface which was fairly primitive - it just used the joystick port on Atari.  Can't remember how the C64 side worked, it would have been either serial or user port.

[+Larry]

Now, back to "why?"  What is your friend wanting to accomplish?  That might help lead to a solution.

[Rybags]

There's very little practical reason to do it.

The default speed is attrocious and like I said it's likely we'd need to bit-bang which would rule out turbo mode unless custom drive side software to do start/stop bit was produced.

The storage advantage isn't really worth it - about 40K advantage over a 1050 ED disk and 10K short of 256 byte DD disks.

Plus you'd have a storage medium that's unique and very few people would want to use it.

[Mclaneinc]

It would be a lot of work, considering the C64 drive has it's controller on board it would need firmware etc etc..

 

Doable, probably, worth the work, not in my book..

[Mclaneinc]

38 minutes ago, Rybags said:

There's very little practical reason to do it.

The default speed is attrocious

That's to do with a problem with the CIA (oops, called it a VIA by accident in first post) in the C64, it and the onboard controller do not play well, hence the rise of fastloaders that worked around the issue, its real speed was actually pretty good but butchered by the 6522. When the non parallel cable fast loaders get going the drive I'd say equals a standard non divisor enabled Atari drive, add something like Dolphin Dos and the cable, and it's a good match for the warp speed Atari drives..

Edited November 22, 2022 by Mclaneinc
Being stupid

[Vyvyan B.]

Aren't those 1541 drives complete crap anyway? You might be better off getting an XF551 board or clone and then you can use a standard PC drive with it. I've been working on something similar using a 3.5 drive.

Edited November 22, 2022 by Vyvyan B.

[Mclaneinc]

The C64 drive mechs are not bad, shame Commodore screwed the drives via the 6522, yes, as standard they are desperately slow, a turbo load tape is sometimes faster, but there were ways around the drive speed released early on.

[+Larry]

One issue is that the power supply was internal to the drive.  That made them big and heavy and HOT.  (Fixed that with the 1541C)  Jiffy Dos and cartridge-type speeders made them quite respectable as goes R/W --  I would say they were as fast as Warp or Ultra Speed drives.  They held a lot of data -- 172K on a SS disk IIRC.  GCR encoding.  There was a lot to like about the C64, but I can't imagine trying to adapt a 1541to an A8.

[Vyvyan B.]

I was under the impression that the 1541 drives were unreliable to an extreme. Was looking through some old article and it said there was a shortage of the drives for a time because so many of them had been returned and that there was some defect in manufacturing.

[Mclaneinc]

I have no doubt you remember rightly, it just does not ring a bell with me. When people talked about the 1541 the thing that deafened all things was the speed, or lack of.

 

Sounds like the first outing of the Xbox and the demonstration pods that shops like us got. No sooner was the Xbox on than it overheated and died..Cue massive recall.. Just a minor mess up (yeah right)

Edited November 22, 2022 by Mclaneinc

[NorbertP]

53 minutes ago, Mclaneinc said:

I have no doubt you remember rightly, it just does not ring a bell with me.

There are two different 1541 drive mechanisms, both of which are prone to failure; the early models had one from Alps which suffered from alignment problems caused by repeatedly smacking the head against a solid stop, and these were later replaced with Newtronics mechanisms that solved that problem but replaced it with a head that is guaranteed to eventually fail due to moisture ingress. As a result, if you're shopping for a 1541 the Alps version is a much safer bet as its problems are merely annoying rather than terminal - realigning the head is relatively easy, repairing a moisture damaged one not so much.

[macsonny]

Wow - this has started a great conversation! The agenda behind my original question was that there were two Indus GT drives on eBay earlier this week but they were the Commodore versions. Hence wondering if there was any way to convert them over to Atari. They ended up going for a stupid amount of money and they weren't even confirmed working!

 

Edited November 22, 2022 by macsonny

[Mazzspeed]

I've owned a number of 1541 drives, as well as a Blue Chip clone drive - I've never had one fail.

 

The Blue Chip drive was a better design then the 1541 however, and 100% compatible.

[Rybags]

Fairly sure the early mechs at least weren't real good.

That's why they chose to use variable geometry and only 35 tracks instead of 40.

[carlsson]

If I recall correctly, Indus used two completely different designs for the GT models, one for Atari and one for Commodore. I think those two have very little in common. Actually the Commodore version seems to use a scrambled 1541 ROM, with trivial instructions in reverse order, possibly some internal routines relocated to different addresses. Things that a non-technical judge in court would not understand were copyright infringements because the binary looked different.

 

Edit: Also early mechs would refer to the 2040 drive for the PET/CBM series, which tend to be read compatible all the way to the 1571. Of course there are custom routines to format 40 tracks on the 1541 for those who want to cram out maximum capacity, but again you'd end up with a partly non-standard disk format.

Edited November 23, 2022 by carlsson

[Mazzspeed]

Using S-JiffyDOS I can format to 40 tracks on an early mechanism, I can also make use of additional blocks in the DIR track 18 for slightly more space.

 

Having said that, I have no real need for 40 tracks TBH. 😕

[Rybags]

Fairly sure the 35 track limitation is just a logical thing and any drive will seek out for the extras.

Though I seem to remember issues with some drives, maybe it was on the final tracks or could have been half-stepping which was more related to copy protection.

[Mclaneinc]

16 hours ago, NorbertP said:

There are two different 1541 drive mechanisms, both of which are prone to failure; the early models had one from Alps which suffered from alignment problems caused by repeatedly smacking the head against a solid stop, and these were later replaced with Newtronics mechanisms that solved that problem but replaced it with a head that is guaranteed to eventually fail due to moisture ingress. As a result, if you're shopping for a 1541 the Alps version is a much safer bet as its problems are merely annoying rather than terminal - realigning the head is relatively easy, repairing a moisture damaged one not so much.

Yeah I was aware of the moisture problem, was watching a YT guy (retrobits I think) explaining the issue and how far people had gone to try and fix it with donor heads from other machines etc (way too much work). I've not looked, but I suspect my recently acquired MK II drive may be the new mech. It was a cheap ebay purchase (yes, you heard me right, a CHEAP ebay purchase  ) so not expecting it to last forever, but it was serviced (with proof) and aligned.  I have a 1541 ultimate II+ as my main drive but got for old times sake an Expert Cartridge which I owned back then but you can't fit two carts in the same hole so needed a real drive, I could have networked to the Ultimate II+ and used it as a drive while unplugged from the cart port but I always wanted a MK II drive and it came along at a great price.

[Tuxon86]

21 hours ago, Mclaneinc said:

The C64 drive mechs are not bad, shame Commodore screwed the drives via the 6522, yes, as standard they are desperately slow, a turbo load tape is sometimes faster, but there were ways around the drive speed released early on.

The heads are self destructing at this point, especially the newtronik one. I had to buy 5 to get one working. I mostly use my 1570 with my C64 now.