For something that "there's no such thing as", there sure are a lot of various null-modem adapters and cables out there.
BTW, while we're picking nits, USB is a serial protocol, so a USB<>RS-232 adapter does have two serial ports! As the name suggests, a null-modem cable/adapter/whatever replaces a serial modem-to-modem connection between two computers regardless of the protocol used; RS-232 and RS-232 modems have been obsolete for decades, so the term 'crossover' has become more popular, but it's the same thing: a cable or adapter to directly connect two computers together. A pair of modems would connect the transmit signal (pin 2 on an M100) on one end to the receive pin (pin 3) on the other end. When you replace those 2 modems (RS-232, USB, whatever) with a null-modem cable you emulate those modems and do the same thing, connect transmit to receive etc. (instead of straight-through, connecting transmit to transmit etc.) Good luck in your quest to eliminate the term "null modem" in reference to USB cables; I suspect it'll be around for a while and more easily understood by many folks than "Provides a DB25M wired as DCE" FWIW, here's a USB-RS-232 Null modem cable; better send them an email to let them know that "there's no such thing" ;-) : https://www.startech.com/ca/Cards-Adapters/Serial-Cards-Adapters/USB-to-Null-Modem-RS232-DB9-Serial-Adapter-Cable-DCE-FTDI~ICUSB232FTN Here's an example of a USB-USB null-modem RS-232 replacement; DTE and DCE have no meaning here whatsoever. https://www.ftdichip.com/Support/Documents/DataSheets/Cables/DS_USBNMC.pdf And here's an Ethernet null-modem (crossover) cable: http://www.nullmodem.com/10BaseT-Crossover.htm m ---- Original Message ----- From: Brian White To: [email protected] Sent: Friday, May 31, 2019 5:56 AM Subject: Re: [M100] possibly ideal serial cable? Technicality: There's really no such thing as null-modem in a usb adapter. Null-modem vs straight through describes the wiring between two serial ports. A usb adapter only has one serial port. That single serial port can be wired to be either a DCE port or a DTE port. Most computers or host devices (like terminals) have DTE ports, and most peripherals (like modems) have DCE ports, so that a modem can connect to a terminal with a simple straight-through cable. Most usb adapters are meant to drop in place of the serial ports that computers no longer have, and so they provide a DTE port. A custom non-standard one could provide a DCE port instead, and could be made even more non-standard by having a DCE port with a female connector. So, it's not null-modem, but it is "Provides a DB25M wired as DCE" ------ Opinion: I personally wouldn't like to combine the serial cable and the usb adapter in one, especially not if the serial port will be so unusual. I don't like uneccessary adapters and connection points, but I do like standard interfaces. So there is a tug of war or a balance between those two aims. I like the usb part to be generically useful on it's own with anything else, and if the usb part breaks, you can swap in any other standard usb adapter. Same for the serial cable. It doesn't have a chip that could go poof, but a wire or a pin could just break. If it's a standard cable, it can be replaced with any other standard cable. I also don't like adapters hanging off of device ports directly. I'd rather have the rigid plug that sticks out of a usb port or a serial port be as small as possible. Aside from being generally less annoying, it puts the least mechanical strain on the port, and reduces the chance that you'll break the usb or serial port in your laptop or other device. So if I have to use adapters, I try to use a standard cable on each device, and stick any adapters in cabling in the middle. Although, those mini adapters that are just like two plugs back to back, a single one of those on an existing plug isn't *too* bad. I also don't like relying on things that are too custom that you couldn't find from other sources or 15 years later. But I myself spent some time hunting down the ususual "ideal" serial cables to document on tandy.wiwk, so that you could have a serial cable that had everything but the usb all in a single cable with no adapters. Partly for the neatness and convenience, and also to document something that a new user could buy and it "just works" even if they have no idea how rs232 works. Those cables are off-the shelf, not made custom by a single person, but they are still non-standard cables that are really only good for this one job. So, I'm guilty of violating that "standard interfaces" rule a little myself, because those cables look like modem cables but they're not. The really ideal minimal as possible arrangement, yet that maintains all standard parts and interfaces all the way, is a standard 9-25 modem cable, a standard usb adapter, and a 9m/9f mini null-modem adapter in the middle. (Except I think no one makes one of those mini-null modems with complete wiring, while some of the cables I found are more complete.) I have to admit, for the purposes of simplicity and removing all the variables that people are mystified by... this does remove all opportunities to get anything wrong, and makes the smallest and simplest object to include in a laptop bag along with the M100. It only does one thing, but if you're only doing this one thing, this is the simplest way to do it. I would put a label right on the plug that says For Model 100 though if I got one. Or at least one that says Port is DCE or something. It's bad to have objects lying around that look like one thing, but are actually something else. If I didn't know the extremely bizarre special purpose this object was wired for (let's say I'm a young relative 10 years from now) and I came across it in a box of junk, and tried to use it, it wouldn't work, I'd watse time spinning my wheels trying things that *should* work, and then throw the thing away. Or I'd stumble upon some combination of adapters that worked, and then I'd think I leaned how serial ports worked except what I learned wouldn't work anywhere else. (and then if I somehow ever found out out that it wasn't broken, it was just wired up in an insane way, I would curse whoever made it, and whoever didn't put big explanatory labels all over it). All that said, it's a cool find and I'll probably get one! For an example of what I mean about not combining too much... Say you don't buy into any of that nonsense I just bloviated so much about, and you like this all-in-one cable because, duh, look how slick that is! Right from the laptop to the m100 in one shot! Now you want to use mComm on your phone instead Laddie on your laptop. Now what? You need... an adapter. You need an "otg" usb adapter to go from the phones usb-c or micro-usb to provide a usb-a port. Do you really want to go back to that guy on ebay and have him make another special cable with a micro-usb on the end instead of usb-a? If not, why not? What was the point of getting this custom cable in the first place? And then next year when you get a new laptop that only has usb-c ports. You need an adapter again, or you need yet another custom cable whose only difference is a usb-c plug on the end... Maybe I won't get one after all because both those last two examples are already true for me. I have an android phone and an android tablet with only a micro-usb. My next phone will probably have usb-c. I already have old and new laptops with both usb-a and usb-c, including one with only a single usb-c port. -- bkw On Thu, May 30, 2019, 4:38 PM Jim Anderson <[email protected]> wrote: I ran across this eBay seller while looking for ham radio programming cables for my various radios - the seller is a ham and makes custom serial programming cables for hundreds of varieties of radios. I did not think to look deeply at his inventory when placing my order with him, but it occurred to me today that he might also make different varieties of regular DB-9 and DB-25 based USB serial cables, and what do you know, he does! One of the cables seems like it might be perfect for our hobby - USB with an FTDI chip on one end, DB-25 male wired null with full handshaking on the other end, and what seems to be a fairly thin and flexible cable in between. The only downsides are that it's a bit pricey ($37 US) and that the DB-25 connector shell he uses may be too bulky to properly fit a Model 100 without cutting extra clearance on the connector shell or the M100 housing (this is a known problem with some cables and the 100, but doesn't affect the 102 or 200). Also AFAIK he only sells on eBay, not through other retailers, which may be a problem for some people. https://www.ebay.com/itm/FTDI-USB-DB-25-Male-Serial-RS-232C-Null-Modem-Full-Han dshake-Cable-NM-25M/151495441948 http://tinyurl.com/y3wln2l3 I really wish I'd bought one while I was ordering cables from him, even just to try it out (it would have been cheaper because shipping to Canada is $$$ and I was getting three cables sent already for the shipping price of one). If I have a reason to buy anything else from this guy I'll definitely get one of these and give it a whirl if nobody else has tried and vetoed it by then. jim
