I’m updating a few of my boards and in the process decided to replace my 1x4 0.1" headers for UART and I2C with something better. QWIIC for I2C seems like a very simple choice. I want to do the same for my UART connector.
I can just use the same JST and label it differently, but before I do I was looking to see if something equivalent to QWIIC exists for UART sockets. A quick scan of QWIIC/Grove/STEMMA seems to be no?!?
Did I miss something?
I did, I did miss something. Finally found that Grove does have a UART equivalent:
Of course this means you can’t connect two Grove UART connectors together without using a crossover cable :-). Ah, the good ole days of DB9 crossover cables vs db9 straight-through cables and the mysteries they brought to us! How I’ve missed them!
Here’s to me, using a QWIIC connector and putting a different signal across it, just so I can contribute my own personal type of chaos to the world of cables and connectors.
If you look carefully
What voltage is your UART running at?
Maybe this is just semantics, but - from my perspective - the QWIIC cable is absolutely not a crossover cable. It’s straight-through, pin-for-pin. Pin 1 is connected to Pin 1, etc…
I too miss the days of RS232 and the knots we could tie ourselves in when trying to decide if our gadget was Data Terminating Equipment (DTE) or Data Communication Equipment (DCE)… Do I need a Null Modem cable or not…?
I was going to use 3.3 to follow QWIIC.
In UART TX has to connect to RX and RX to TX, unlike I2C where SDA goes to SDA and SCL goes to SCL. So this cable, used for two UART ports, would have to have one end be black/red/blue/yellow and the other would need to be black/red/yellow/blue. That’s what I mean by ‘crossover’.
So not only is the line signal different, but the cable wiring is too. That’s ok in my scenario, because I’m not using this as a ‘board to board’ connector, but a ‘board to usb ttl uart receiver’, and I’ll connect via the female jumper cable and manually swap rx/tx.
@TS-Russell here’s some wiring diagrams from the ‘bad ole days’ that show what a ‘null modem’ cable does:
Man, those were complex times…
Some of us that keep 45 year old legacy systems running get to deal with this on a daily basis!
Awesome; 3.3v is good to go with qwiic wire gauge size…some UARTS attempt much higher voltage/power ranges!
I agree after re-reading; I think I mis-spoke. I was attempting to speak toward the specific use in this situation and mis-represented the actual pin-to-pin interactions if comparing the cable to itself…which definitely make it not an actual crossover. Though happily, It will work the way jay wants, as far as I understand things here lol
Part of my profession role is to support lab and industrial comms which do often still use RS-232. For better or worse, it’s a proven winner that has stood the test of time, frustrating at first, robust in the long term, Microsoft-update proof, able yet primitive. I’ve come to think of TX/RX as output/input or, if you like, mouth and ear. That DTE/DCE nomenclature is from before my time and I’ve never been fully comfortable with it and it does still turn up at times like the colorful drawing above.
Even in day-to-day public settings, you can see serial devices all over the place. Common ones are remote displays like the ‘Now Serving’ sequential dealie at the deli or the ‘amount tendered’ display on a toll collection kiosk. A lot of receipt printers and paper journal or line (that slip stapled to your takeout bag) and self adhesive label printers (the little sticker on the windshield after an oil change) are serial.
