Is there a way to figure out which pin is RS232 TX and which is RX with a multimeter?

[ryanc@infosec.exchange]

@catsalad @retr0id @whitequark ಠ_ಠ

[gsuberland@chaos.social]

@ryanc @retr0id @whitequark add a 4.7k pulldown to ground, idle voltage on TX will remain asserted negative (-3V at least) with respect to ground whereas RX will pull to 0V.

[yurigaga@mastodon.social]

@ryanc @retr0id @whitequark what is your setup? What are you connecting to rs232?

[ryanc@infosec.exchange]

@gsuberland @retr0id @whitequark I've got a 0 V and a -6.6V

[gsuberland@chaos.social]

@ryanc @retr0id @whitequark -6.6V is TX from the device then (spec is -3V to -15V)

[ryanc@infosec.exchange]

@gsuberland @retr0id @whitequark Fantastic, thank you.

I've even figured out how to get the wire that wants to be YGRK crimped in as RYGK so that it won't be confusing to wire up the other side.

[endlessmason@hachyderm.io]

@ryanc
Can you spam FF00 and see which one has a square wave?

@retr0id @whitequark

[ryanc@infosec.exchange]

@EndlessMason @retr0id @whitequark i figured it out. I think. I don't have sufficient control over the device to do that.

[endlessmason@hachyderm.io]

@ryanc
Might put this toot on the back of a hoodie, it seems to apply pretty widely to my life.

@retr0id @whitequark

[ryanc@infosec.exchange]

@yurigaga

Vent Axia ventilation systems. They've got a 4P4C modular jack with 5 V, RS232 TX/RX and ground, to which you can connect what is effectively a "dumb terminal" with four keys and a 16x2 character display.

I'm going to set up an ESP8266 as a serial bridge, write a terminal emulator for it, and see about operating it via screen scraping.

[ryanc@infosec.exchange]

@EndlessMason @retr0id @gsuberland The interface works.