Speaking of “flow control”, while you would not need it if you only use special software like HTERM, I suggest getting a serial adapter that also implements *“software flow control on-chip“*. If your adapter has it, 19,200 bps is no problem for the built-in TELCOM software. If your adapter lacks it, programs that use software flow control cannot keep up when receiving data quickly. When that happens, the Model-T will send the XOFF (“transmission off”) character asking the remote host computer (your Mac) to pause, but with many modern serial adapters, the message will come too late and your Model-T will have to discard bytes, leading to corruption either on the screen or in downloaded files. Details
Back in the day, this feature wasn’t necessary and “software flow control” was truly handled by software and the response time was quick because the chip that implements the serial hardware, the “UART”, only held a single byte at a time. If your Model-T sent the XOFF character to a host in the 1980s, the host would stop almost immediately. Over the years, to allow for ever higher speeds, newer UART chips have grown huge pipelines (“FIFOs”) to buffer the data. The problem is that in the time it takes the XOFF character to pass through a FIFO on the way to the host computer, the host has already filled the FIFO going the other direction with characters for the Model-T. When the host stops sending data, there is already too much in the FIFO and our vintage hardware will drop bytes. In contrast, if you get a UART with software flow control on-chip, also known as “hardware XON/XOFF”, this isn’t a problem. Before each byte is placed in the FIFO, it is checked if it is XOFF. If it is, data going the other direction is immediately paused. I usually stick with UART chips manufactured by FTDI because the most common ones have that feature. However, there are also a lot of fake FTDI cables available on Amazon, so check the negative reviews. I got a genuine FTDI usb serial adapter years ago from some small retro shop. (ArcadeShopper.com? A2Heaven.com? Neither of those seem to carry them now.) —b9 On January 18, 2026 12:36:42 PM PST, “Brian K. White” <[email protected]> wrote: These cables are known good. > > http://tandy.wiki/Model_T_Serial_Cable > > And the blurb at the top explains why the 100 is weird and what you need and > why any other cable you got is probably wrong, and what adapter to get if you > want to use that cable anyway. > > There are actually one-piece usb cables but as a personal preference I don't > recommend them because that kind of adapter is essentially "wrong" for every > other serial usage in the world. You would need either a null-modem adapter > and/or a gender-changer adapter to make it work with anything else but a 100. > Also the single piece usb cables I think are only hand made ones on ebay. > There might be real factory ones but super rare. In fact the few I've seen > were actually just mis-labeled and were actually parallel ports. I'm not sure > I've ever seen one other than home made. > > I'd rather have a usb-serial adapter that was standard, providing a standard > port, exactly the same as what was on the back of old motherboards for about > 30 years, and have the special wiring just be in the serial cable. Those > kinds of cables are uncommon, but are still more common than a usb-DCE-female > cable. As you see above I found several off the shelf factory cables. Some > with full handshaking (real flow control) and some more with only 3 wires > plus the dtr/dsr loopbacks (fake flow control) already in the ends. > > Just my suggestion. > > > On 1/18/26 12:51, Erik van der Tier wrote: > >> >> Hi, >> >> I’ve been trying to get my T102 to talk to my modern MacBook. For this I’ve >> bought a usb-c to db9 cable and a db9 to db25 serial null modem cable. I >> have today installed a REX# in my t102 as well. >> Anyway, I haven’t been able to get a connection to a terminal program nor >> TS-DOS. I know this *can* work on a Mac as I”ve previously had a T102 and a >> pretty crazy franken-cable that work like a charm. >> >> This time I though, I’d get a simpler setup with only one usb-c to serial >> and a null modem cable, in stead of a USB-A to serial, a DB9 serial modem >> cable, a null modem converter and a DB9 to DB25 converter. Crazily enough >> that horrible mess of cable and multiple adapters worked. >> >> The serial cable that I got this time around is this one: https:// >> www.amazon.nl/Vrouwelijk-parallelle-printerkabel-Datatransmissie- >> Communicatie/dp/B08C9TXXCK/ref=sr_1_18? >> __mk_nl_NL=%C3%85M%C3%85%C5%BD%C3%95%C3%91&crid=TRBHXQVKSIVH&dib=eyJ2IjoiMSJ9.NOI_htfBsniWi16cA7NrpAsbwAFQHVL9HsjtCZDB-QrcH328-7sC_CZHghnU9G19bemEAqjGO2AYpuVod7RPWDwXiMs-6romUKb81fCynFFx7v8y0LYEfR77WCc9mMFZOu_J2ZEZXMmzgzG4UVOAP2-9q0vmmPaW_Ko3ivHRWYh5ZifAD_7KLGEqK7aFxOn22KcARopde7vuFHpTzbvko1rPviFqUyTirH8GS7y8mj4GWrIXFhwTAiFCo6ZOaSuwTLUTNk1apT1lg5p8hgHYLzKCiN7PfDL-dWWzZUZDUfE.wnq2KLE6yCDlC49ZLZqqn82UL8RLijAKlOy-veK9Jtk&dib_tag=se&keywords=Tripp+Lite+Model+P456-006+6+ft.+Null+Modem+DB9F+to+DB25M&qid=1768668965&sprefix=tripp+lite+model+p456-006+6+ft.+null+modem+db9f+to+db25m%2Caps%2C113&sr=8-18 >> >> <https://www.amazon.nl/Vrouwelijk-parallelle-printerkabel-Datatransmissie-Communicatie/dp/B08C9TXXCK/ref=sr_1_18?__mk_nl_NL=%C3%85M%C3%85%C5%BD%C3%95%C3%91&crid=TRBHXQVKSIVH&dib=eyJ2IjoiMSJ9.NOI_htfBsniWi16cA7NrpAsbwAFQHVL9HsjtCZDB-QrcH328-7sC_CZHghnU9G19bemEAqjGO2AYpuVod7RPWDwXiMs-6romUKb81fCynFFx7v8y0LYEfR77WCc9mMFZOu_J2ZEZXMmzgzG4UVOAP2-9q0vmmPaW_Ko3ivHRWYh5ZifAD_7KLGEqK7aFxOn22KcARopde7vuFHpTzbvko1rPviFqUyTirH8GS7y8mj4GWrIXFhwTAiFCo6ZOaSuwTLUTNk1apT1lg5p8hgHYLzKCiN7PfDL-dWWzZUZDUfE.wnq2KLE6yCDlC49ZLZqqn82UL8RLijAKlOy-veK9Jtk&dib_tag=se&keywords=Tripp+Lite+Model+P456-006+6+ft.+Null+Modem+DB9F+to+DB25M&qid=1768668965&sprefix=tripp+lite+model+p456-006+6+ft.+null+modem+db9f+to+db25m%2Caps%2C113&sr=8-18>. >> >> I don’t really know much about serial cables and connections, so I’m having >> a hard time debugging this setup. Does anyone of you have an idea of what’s >> wrong, or what serial null modem cable that can be ordered in Europe and is >> know to work? >> >> Cheers, >> Erik >> > > >
