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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