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I want to use a CH340G USB UART to connect to the console of my raspberry pis - something like this: http://www.ebay.com.au/itm/To-TTL-USB2-06Pin-CH340G-Converter-for-STC-Arduino-PRO-Instead-of-CP2102-PL2303-/191149156465 (sorry for the ebay link, but I could not find anything more permanent. Please comment if you have such a link).

Hooking up TxD, RxD and GND are easy. I want to be able to use the DTR signal to reset the RPi. If I turn on DTR, I want that to go to a pin that will cause the Pi to reset. This makes this little USB UART useful as a low-level device access mechanism, accessing the serial console (and with u-boot, it can hook into the boot process), and a reset line if things go bad.

I do not want a user- or kernel-level mechanism to detect this and do the reset. I'd like it to be at the hardware level so I can reset at any time regardless of the state of the software.

I also do not want to use a watchdog. I would like a crashed Pi to keep its last error message on the console and allow me to reset manually.

How can I hook up the DTR line to do this?

Edit: I have RPi Model B rev 2.0 and RPi2 boards.

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  • Also, what's a cool thing I can hook up CTS to for the Pi to signal back to the controller host?
    – camh
    Commented Jul 22, 2015 at 7:09

1 Answer 1

Reset to default
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You can use the P6 pins in the Raspberry. Take a look at http://raspi.tv/2012/making-a-reset-switch-for-your-rev-2-raspberry-pi for details.

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  • Thanks, but how would I hook up the DTR signal to do that? That page describes a switch. I don't want a physical switch, but a remote reset via raising DTR.
    – camh
    Commented Jul 22, 2015 at 8:39
  • So, Pin1 is ~3V, Pin2 is ground. If I hook up the DTR line to pin 2, it should reset the Pi when I assert DTR... I think. Also, the Pi2 has a similar header called "Run" at the opposite end to the USB connectors.
    – camh
    Commented Jul 22, 2015 at 9:00

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