Yes, except most generic level shifters (like that sparkfun one) don't have enough channels to do all the flow control lines, so you might get rts/cts but not dtr/dts. I did hunt up some special ones that do have enough channels, but I haven't tried to actually make an adapter out of it yet. For one thing it needs a power source which might not be doable just from parasitizing the serial port itself.
The original real cable and the Marty Goodman one does not require a power source, because it does not bother to do full proper level shifting, it just relies on a trick which happens to work on a M100. I think a max248 or similar would be ideal, except max248 has actually more channels than necessary, but it has all the charge pump caps built-in so it just needs 5v, which might possibly be scavengable from a control line from the pdd, or from the m100 with additional parts to knock down from a +12v signal. Don't quote me on the exact most ideal part number. In the end, the diode cable ends up looking most practical after all because it sidesteps the whole issue of a power source. Not to mention it's probably easier to physically solder and package up 3 diodes in a cable vs a 20-pin soic chip. But I do still want to try to make a true proper full rs232-ttl cable sometime just for the heck of it. On Feb 27, 2018 7:42 PM, "Josh Malone" <[email protected]> wrote: > 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 >> >> >>
