| Posted By
Crown
on 2003-09-08
|  Strange 1551
Check this out
http://cgi.ebay.de/ws/eBayISAPI.dll?ViewItem&item=3045320959&category=3543
Check the back side of the 1551, there is two IEC connector on it, and the parallel interface cable is not there, just a hole left. Is this a custom modification, or did Commodore actually sold a version of the 1551 with the IEC connections, and without the plus4 parallel interface? Really strange. I've seen an other auction before, where a C64 was sold together with a 1551, but seeing this one it starts to make sense....
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Posted By
JamesC
on 2003-09-08
| Re: Strange 1551
I will bid on this, and if the seller will not ship to me here, then I will have it sent to SVS for analysis. This could be one of the fabled 1542 disk drives, mismarked, or it could be the work of a person who customizes their equipment.
I had considered making my own 1542 by putting the 1551 DOS into seperate ROM chips and plugging them into a 1541 board, then painting the case to match, but I have other projects that are higher up the list.
My eBay user ID is 'cbm264' so please don't bid me up on this, okay? 
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Posted By
Crown
on 2003-09-08
| Re: Strange 1551
Ok, so then I'll wait posting about this to the cbm-hackers list until the auction is over.
I've looked around to find some information about the 1542 but there was not much. Only that it is a 1541 in the color of the 1551, and that is supposed to better then the 1541 somewhat, but no more detail.
I don't think you can make a 1541 by putting the ROM of the 1551 into a 1541 board, the 1551 communicates through a parallel port, while the 1541 through a serial port, the transfer routines wouldn't work. It is also possible that the 1542 had a 2Mhz CPU like the 1551.
Here is the other auction where I've seen this drive
http://cgi.ebay.de/ws/eBayISAPI.dll?ViewItem&item=3042338928&category=3544
This also says that it handles about a 1551 drive, but I don't see the cartridge of the 1551 anywhere on the picture.
I've also read that there was plans to make the 1551 available for the C64, but all the sites were speculating on how would that happen, whether Commodore would add a cartridge based parallel module with it. It is completely possible that they've actually released the 1551 with the serial port and that was the C64 compatible version, and didn't gave it a different number. In that case inside it would be the same as the 1551 probably with the 2Mhz CPU, but with a different ROM....
If you get this, the ROM should be dumped and sent to Marko Makela to put it up on the ftp.funet.fi site.
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Posted By
JamesC
on 2003-09-08
| Re: Strange 1551
Regarding the second auction you posted, I presume that the seller has simply mismatched the disk drive with the computer, not knowing that they are not compatiable.
Commodore dropped the TCBM standard (and hence development for the parallel disk drive for the C64) when the 264 series was dropped. The only reason 1551s were sold in any quantity in Europe is because of all the 264's being dumped there. The 1551 was never released here because the computers were quietly pulled from dealer shelves in March of 1985, after only 6 months on the market. With the 128 soon to appear on the horizon, Commodore didn't want upset dealers refusing to carry yet ANOTHER orphan machine.
And THAT'S why the 1542, or a TCBM drive for the 64, never appeared. When the Tramiels left, the computers were shoved out the door only to recover development costs and fulfil minimum sales commitments from the software suppliers (Tri-Micro, Scott Adams, Island Graphic, etc).
Itonically enough the idea was persued here in the States by an independent company. If you can find a Lt. Kernal hard drive, it uses the C64's parallel port directly, instead of the serial port or an IEEE adapter. With a 10 meg hard drive, it sold for US$1000.
Another thought as to why the TCBM standard wasn't persued by Commodore -- there were several companies that sold cardridge port expansions here.... add two, three, or 4 cartridge slots to the C64, add in am operating system that doesn't directly support the parallel disk drive to start with, and system stability becomes eerily Windows-like in its' kludges, core code upgrades, and work-arounds.
As I've mentioned before, Commodore US released all Plus/4 disk software with copy protection code dependant on the 1541's ROM. Evidently Commodore software development knew something that Commodore marketing did not.
Regarding the 1551's ROM, all the ROM code does is read info from the disk and put it in a buffer, and pull information from a buffer and write it to the disk. It's the other chips and wiring in the system that makes the drive serial or parallel. If the same code is run on a 6502 as opposed to a 6510, the code itself doesn't know that it's running slower. Evidence: 1551s run in the US without any 50/60Hz adjustments (well two of the three known 1551s, mine is still acting very strangely). As long as the proper voltage is coming out of the transformer, the disk drive merrily lights up and turns the disk, reads or writes just as a 1541 is expected to. Bo Zimmerman and Jim Hehl made no internal mods to their 1551s to make them work here.
Even if it doesn't work, it would make a nice experiment. 1541s are cheap enough here to try it; I have 2 plus 2 1541-IIs to experiment with.
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Posted By
Crown
on 2003-09-09
| Re: Strange 1551
According to Bo Zimmerman's list the 1542 was a serial drive and not a TCBM device.
You are wrong about the 1551 ROM, the hardware in this drives are not like you imagine, there is no additional hardware which magically takes the content of a buffer and pushes it through a serial or parallel channel, this is all done by the CPU with code in the ROM. In case of a 1541 every bytes is decomposed to bits, and each bit is sent individually through the serial IEC protocol, but it is basically the CPU manipulating the wire directly. In the 1551 it is sent through a parallel port, but this is also done with the CPU, but the code is different...
Speed of these machines are not dependant on the frequency of the power supply, first of all the power is converted from AC to DC and in DC land you see nothing from the frequency of the AC signal.
Speed is decided by the clock crystal, and drives released in the States and in Europe has the same crystal, that's why you don't need any modification.
Anyway I got response from the seller, and he told me that this is not a custom modification, but it was sold this way in the shop, so this confirms for me that this is the C64 version of the 1551 drive, and probably was only released in Europe (could be Germany only), and most likely in small quantities as there is no word about its existence on the specialized commodore sites....
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Posted By
JamesC
on 2003-09-15
| Re: Strange 1551
Following up on this auction.....
I received an email from C64doc in Germany about this auction. He stated that this was simply a 1541 in a 1551 case (the serial holes were cut by a previous owner and 1541 internals inserted). I followed the email address back to forum-64.de, entered the forum there, and C64doc had just left about 12 minutes prior. Another forum administrator, AC, entered and was kind enough to ring C64doc to tell him to reenter the forum.
C64doc attempted to reach the seller to try to get our bids retracted because the disk drive is not as described, but the seller either didn't get our emails in time or didn't want to retract them. It didn't matter either way because another German user popped up at the last minute and outbid the EU35,00 that I had bid when I thought this was some rare device.
I had a nice conversation with Doc and AC, as well as a couple other people who popped in during the two hours I sat in this German chat room. I would like to thank everyone for switching to English just so that I could follow the conversation.
I also made some friends that will make the transfer of future Ebay items simpler. I will be looking for NTSC 2002 and 1084 monitors (inexpensive but working) while they will be looking for 1551s (again inexpensive but working). I see a major increase in my postage costs in the future, but it will be worth it for some of the things that seem to have disappeared not long after the Plus/4 was removed from store shelves 18 years ago.
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