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The Serial TTL connector we deserve

kohlschuetter.github.io

11–20 of 80 posts

Re: The Serial TTL connector we deserve

#11

Nice but it’s huge! I’d prefer something smaller like these 3 pin magnetic connectors from Aliexpress. https://a.aliexpress.com/_c4CtK0gj

And where do I put Vref, RTS, CTS, and plug detect? That's 7 pins ;)

Less of a joke though: those aren't polarized, how do you not accidentally 180° them? Are they magnetically polarized or what?

[ed.: I didn't initially see it, they're mechanically polarized, one "short end" is flat, the other rounded.]

Re: The Serial TTL connector we deserve

#12
post #10
post #9

Earlier quoted context omitted.

That really sucks for hotplugging since TRS connectors sliding in basically make random connections before seating properly. Granted, you shouldn't hotplug TTL serial, but everyone™ does it anyway. (In some situations you're even forced to, to avoid reverse powering something.)

They're not random connections; they're predictable. I'm not worried about Tx briefly touching Rx or ground in these devices.

Random in the time sense. You'll get junk on your serial line, depending on the scenario that can matter a lot.

Re: The Serial TTL connector we deserve

#13
Ideally you wouldn't need to expose a TTL serial debug port to begin with. Maybe on a prototype you would want this but I'd rather just have a single connector that can expose everything (jtag or swd). Bonus points if the interface chip is on the board so it's just a USB port

Re: The Serial TTL connector we deserve

#16
I always wonder why Molex makes only black and white connectors. This makes it needlessly difficult to use different connectors for different purposes. Same with phoenix contact but there it's mostly green terminal blocks. Is it so difficult to just offer some more colors?

Re: The Serial TTL connector we deserve

#17
post #13

Ideally you wouldn't need to expose a TTL serial debug port to begin with. Maybe on a prototype you would want this but I'd rather just have a single connector that can expose everything (jtag or swd). Bonus points if the interface chip is on the board so it's just a USB port

FUSB307B is amazing for this, it has a hardware DBG output pin indicating that a USB-C debug accessory mode connection has been made. Perfect for connecting a mux and putting SWD & serial on some USB-C pins.

Too bad there's no standard for debug accessory connections. Also, at that point (putting a USB-C TCPC on your board) you might as well do full usbserial…

NB: there's no orientation detection in debug accessory mode.

Re: The Serial TTL connector we deserve

#18
I would tell anyone who is doing a new traditional serial connector/cable to add the following -

1. Automatic DCE-DTE detection and an interface which will rewire itself as needed to be the correct way, or you automatically know DCE vs DTE by connector gender.

2. Automatic Voltage Detection - 232 levels, TTL 5v, TTL 3v - and interfaces that are isolated enough to deal with the wrong voltage (clamping diodes or whatever), or different cable sizes for each.

3. Automatic type detection - TTL/RS-232, RS-422, RS-485, or different connector types by each.

Ideally I'd do this on a 8p8c or 10p10c connector, because of ease of making cables, with various resistance values across pins 1-8, or 1-10 to tell you what kind of interface it was.

Re: The Serial TTL connector we deserve

#19
post #18

I would tell anyone who is doing a new traditional serial connector/cable to add the following - 1. Automatic DCE-DTE detection and an interface which will rewire itself as needed to be the correct way, or you automatically know DCE vs DTE by connector gender. 2. Automatic Voltage Detection - 232 levels, TTL 5v, TTL 3v - and interfaces that are isolated enough to deal with the wrong voltage (clamping diodes or whatev…

At that point it's not a debug connector anymore. Note there's a pseudo-standard for V.24/RS232 on RJ45 already, and nobody uses it for debug connectors since (a) you'd need a RS232 transceiver and (b) RJ45 connectors are honking huge.

The point is to shave off the last cent, which is why you get a possibly-unpopulated 1×4 or 1×3 2.54mm header. Bonus points if the manufacturer designed series resistors into the board (let's say 0402 or even 0201) and left those out too to save the last 0.01 cent.

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