A proper level-shifter breakout would do the trick, right? https://www.digikey.com/product-detail/en/sparkfun-electronics/BOB-11189/1568-1193-ND/5673779
On Feb 27, 2018 7:21 PM, "Scotty Brown" <[email protected]> wrote: > Thanks for the info gents. > > It appears I should have done a little more research on the cable. > > Will give this a go and report back (still would love an original cable is > anyone has one!). > > Cheers, > > Scotty > > On 28/02/2018 08:50, Brian White wrote: > > The cable requires at minimum a few diodes, besides the necessary pin to > pin wiring. > The real original cable appears to use resistors and transistors, and > there is a schematic someone came up with a long time ago that uses diodes > and resistors, and at least one person has claimed since then that they > made a cable that works fine with only the diodes. > > The complicating issue is that the PDD is TTL (0-5v) while the serial port > is rs232 (-12v-+12v), and the fact that you can usually get away with a lot > when interfacing with rs232 and techgnically violate the spec and yet it > still "works", and the fact that part of the scheme in our case is > particular to the actual wiring of the rs232 plug in the M100 where there > are pull-down (or pull-up, I forget which) resistors on some of the flow > control pins in the M100, which ends up causing the signal to be valid high > or low for rs232 merely by blocking it, without having to actually DO the > proper electrical conversion you otherwise would have to in the cable. IE, > the unofficial cable schematic merely one-way-blocks some signals with a > diode, which technically does NOT produce a valid rs232 signal level (-3v > to -25v or +3v to +25v), but, because of the internal pull-downs in the > M100 on those pins, merely blocking the signal in the cable ends up hving > the result that the pull-down in the M100 pulls the signal down to a valid > level. So, a cable that works between a PDD and M100/102/200, is not > guaranteed to work between a PDD and any other pc serial port or usb serial > adapter, although so far, they do seem to be working everywhere. > > Links to the unofficial schematic, and the service manual which shows the > pinout for the PDD end of the cable: > http://tandy.wiki/TPDD > > > > On Tue, Feb 27, 2018 at 4:38 PM, Scotty Brown <[email protected]> wrote: > >> Hey all, >> >> I've just got back into my M100 over the last few months - have been >> blogging about it a little here: https://scottyau.blogspot.com.au/ >> >> I've pulled a lot of stuff out of the mailing list archives - thank you >> all so much. >> >> I've managed to get my hands on a Portable Disk Drive 2 - however it >> didn't come with the serial cable. >> >> Chances are I can probably find a pin out and make one - but I wondered >> if anyone on list had an original cable they would be willing to part >> with (for a fee + postage of course). >> >> Cheers! >> >> Scotty >> >> > > > -- > bkw > > >
