Re: VIA shift register

From: Terry Raymond <traymond160_at_gmail.com>
Date: Thu, 10 Jan 2019 18:09:10 -0700
Message-ID: <CAJ+D7=PAgmrxWYPimKNxaWK+HLts3mkG_E6DGA0gwaEagKGZBA@mail.gmail.com>
You can find more up to date C64/C128 schematics on Ray Carlsens website.
Ray resides In U.S.A. in Washington repairs most 8-bit Commodore computers.

On Thu, Jan 10, 2019, 1:33 PM Francesco Messineo <
francesco.messineo@gmail.com wrote:

> On Thu, Jan 10, 2019 at 8:51 PM Pasi 'Albert' Ojala <a1bert@iki.fi> wrote:
> >
> > On 01/10/19 18:52, Francesco Messineo wrote:
> > > On Thu, Jan 10, 2019 at 5:33 PM Pasi 'A1bert' Ojala <a1bert@iki.fi>
> wrote:
> > >> On 10.01.2019 17:22, smf wrote:
> > >>> On 10/01/2019 08:11, André Fachat wrote:
> > >>>> I know this solution, but IIRC this prevents bidirectional operation
> > >>>> without extra direction control.
> > >>> Don't the c128 & 1571 have extra hardware for direction control on
> the
> > >>> 6526 ?
> > >> http://www.iki.fi/a1bert/Dev/burst (already mentioned earlier, but
> this
> > >> is the "forever link"):
> > >>
> > >> "The C128 hardware includes a buffer driver between SRQ and the
> cassette
> > >> read line so that cassette activity or cassette drive presence will
> not
> > >> disturb the fast serial port. It also has a two-directional buffer
> that
> > >> connects SRQ and DATA to the CIA1 synchronous serial port. The
> direction
> > >> is controlled by the MMU chip. These buffers are required to hide the
> > >> fast serial connection is C64 mode."
> > > I can't find this bidirectional buffer in the C128 schematic
> > > (zimmers). Wrong schematic?
> >
> http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/c128/310378-3-left.gif
> >
> > See CIA1 SP and CNT, U58 and U60.
>
> yes I see that, they didn't use a bidirectional buffer anyway :) They
> gated the signals through open collectors NANDs.
> Ok, result is very similar, in C64 mode, they prevent the signals
> reaching the serial shifter of CIA#1.
>
> >  From my article: "Theoretically you should be able to make the
> > modification work with C128 in both modes by first connecting the wires
> > and then cutting/bending up U58 (74LS03) pins 3 and 8, and U60 (7407)
> > pins 6 and 8. This disables the C128 fast serial hardware and the added
> > wires will perform their function in C128 and C64 modes. I have not
> > tested this, so if you try it, I would be very interested in your
> results."
>
> I would not modify a C128 as you suggest. I'd try lifting U8P9 and
> just use the same routines used in C128 mode (of course they would
> need to be copied somewhere in the C64 RAM first).
>
> Frank
>
>
Received on 2019-01-11 03:00:03

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