Some tips on that.... Are you using Linux on the Pi? If so, it would be easier to just use a USB serial port. The Prolific and FTDI ports both work with Raspbian; I've used both.
Otherwise, maybe look at a DTE wired level converter with CTS/RTS.... like this one: https://www.amazon.com/NulSom-Inc-Ultra-Compact-Converter/dp/B00OPU2QJ4/ref=sr_1_4?dchild=1&keywords=ttl+rs-232+level+converter&qid=1600718673&sr=8-4 Although I'm not sure where you'll get CTS and RTS on the Pi. I don't know that it's mapped to any of the GPIO pins. This might help a little bit: https://www.raspberrypi.org/forums/viewtopic.php?t=241623 Tom Wilson [email protected] (619)940-6311 K6ABZ On Mon, Sep 21, 2020 at 12:10 PM Jonathan Yuen <[email protected]> wrote: > Hello, > > I actually am trying to connect a Psion 5MX with it's 'serial cable' to a > raspberry pi, the serial lines on the GPIO thing. The pi is TTL, so I have > an adapter to change it to RS-232. The adapter is DCE, but the Psion cable > actually terminates as DCE, since it was made to plug into the serial port > on your PC for synchronizing etc. The Psion has a perfectly good comm > program, so I'm using it as terminal (there is even a VT100 program) but I > need the 'null modem' or crossover connector to connect it to the > level-shifter. Since they were both female, I actually did the test with 3 > pieces of maybe 14 or 16 gauge insulated wire, maybe 3 cm long, with their > ends stripped and pushed into the right holes. But I thought I should have > something a bit more 'robust' and maybe do the other lines as well. > > I think Psion actually made a modem that connected to this cable, but that > must have been DTE....... > > I guess I always thought of the 'modem' in null-modem as 'modem=DCE' since > I've always connected DTE things together. But I appreciate the feedback > from the group. > > Jonathan > > [email protected] > ________________________________________ > Från: M100 [[email protected]] för Tom Wilson [ > [email protected]] > Skickat: den 21 september 2020 20:18 > Till: M100 Mailing List > Ämne: Re: [M100] definition of null modem > > "Null" means "none" or "zero." So "null modem" means "no modem." > This term is an adjective and should be coupled with "cable", "adapter", > or some other noun to be of any use. > > I don't see a need to re-define the term, since "null modem cable" is well > established, and we all know exactly what the term means. > > Strangely, there are times you actually need a null modem cable to connect > a computer to a modem. Most CP/M computers used dumb terminals, as did any > mainframe and minicomputer (also called a mini mainframe.) Since those > computers were designed to have DTE devices plugged directly in to their > terminal ports, you might need a null modem cable to connect a modem to the > mainframe... Of course, in that case, we'd just call those "modem cables" > (or, more commonly, the 8-pin modular to DB25 adapter would be labeled > "modem".) So in that instance, we literally used a null-modem cable to > connect to a modem.... > > Sometimes I love the English language. > > Tom Wilson > [email protected]<mailto:[email protected]> > (619)940-6311 > K6ABZ > > > On Mon, Sep 21, 2020 at 9:16 AM Lee Kelley <[email protected]<mailto: > [email protected]>> wrote: > I've always thought "null modem" was a misnomer. It probably should have > been called a "non modem cable" or simply a cross over cable as mentioned > above. > > On Mon, Sep 21, 2020, 11:06 RETRO Innovations <[email protected] > <mailto:[email protected]>> wrote: > On 9/21/2020 10:59 AM, Jonathan Yuen wrote: > > > > That said, I could only think that the other wiring should be same as a > null modem, but I thought that I should air my thoughts to see what other > people think. > > I'm curious about the use case, but you are correct, the wiring would be > the same. Maybe, (though no one will do this, as the other terms have > been in use for too long), it's best to call such a cable a "crossover" > cable, like is available for Ethernet ports. > > Jim > > > --- > När du skickar e-post till SLU så innebär detta att SLU behandlar dina > personuppgifter. För att läsa mer om hur detta går till, klicka här < > https://www.slu.se/om-slu/kontakta-slu/personuppgifter/> > E-mailing SLU will result in SLU processing your personal data. For more > information on how this is done, click here < > https://www.slu.se/en/about-slu/contact-slu/personal-data/> >
