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/>
