Re: IEEE-488 adapter for 1541

Hi Jeffrey,
I've never went further than the schematic phase on my project, but
the only difference (for this particular case) between a 1541 and
1541C is that the -C has a single 16kbytes ROM instead of the 2 x
8kbytes ROMs of the old 1541. It can however run the same firmware as
all the memory mappings are the same. The original 1541C ROM has an
additional CS2 line tied to +5V on pin 27, so to install a dual
firmware, you can simply use a 27256 EPROM with pin 27 left outside
the socket and connect it  to any of the power rails via a 4k7
resistor, then connect a switch to the same pin that goes to the other
supply rail. So you can select either the lower 16K half or the upper
16K half of the 27256 (its pin 27 is A14). On one half you can burn
the original 1541C (or any other 1541's version) firmware and on the
other half, the complete 2031 firmware.
The daughterboard going into the 6522 socket is the same for all the
1541 versions.
It's just easier because you don't need an adapter to substitute the
original 2364 ROMs of the 1541. Also 1541C tend to be cheaper (the
same apply to the 1541-II, but this one has less space inside the
case) than the 1541 and often they have a mechanic with a track-0
sensor (that you enable by cutting JP3, but it needs the right
firmware to be effective, and also I've seen some 1541C without the
sensor installed) that it's really good to avoid the infamous track-0
sound when a formatting starts or in case of read errors.
As I said, I abandoned the conversion project because I'd rather have
a write compatible unit with the 3040 that I'm now sharing between my
PETs.

On Sat, Apr 6, 2019 at 7:25 PM Jeffrey Birt <birt_j_at_soigeneris.com> wrote:
>
> Hi Frank,
> Do you have any more information about converting the 1541C?
>
> Jeff_Birt (Hey Birt!)
>
> -----Original Message-----
> From: Francesco Messineo <francesco.messineo_at_gmail.com>
> Sent: Saturday, April 6, 2019 10:37 AM
> To: cbm-hackers_at_musoftware.de
> Subject: Re: IEEE-488 adapter for 1541
>
> Hi Jeffrey!
> I also started some years ago my own project for converting a 1451 into a 2031LP, of course with switchable kernel and maintaining both ports. A daughterboard is quite an easy thing to add to the 6522.
> However I realized that 1541 format isn't write-compatible with the 3040/4040, so at least for me it wouldn't allow me to share the same disk (well, share in read only mode, yes) between my PETs.
> Converting a 1541C is way easier anyway, you don't need a ROM adapter, just a 27256 and a switch and you can re-use the 27128 socket on the 1541C motherboard.
>
> Frank
>
> On Sat, Apr 6, 2019 at 5:31 PM Jeffrey Birt <birt_j_at_soigeneris.com> wrote:
> >
> > Saw this posted on they Lemon64 forum, thought it was an interesting project.
> >
> >
> >
> > https://dl2dw.de/en/diy-projects/commodore/50-trimod-cbm-adapter
> >
> >
> >
> > Jeff_Birt (Hey Birt!)
>
>
>
>
>