Can Serial TX Pin be put in Open Collector Mode?

prices · May 16, 2015, 5:30pm

I need to interface the spark Photon/Core to Atmel XMega chips that are using the serial one-wire that some (maybe all) XMega devices are capable of. Basically, it puts the serial port TX pin in open collector mode with a pullup, then internally connects it to the RX Pin.

If I can get the TX pin on the Photon/Core to be in open collector mode, I can externally connect them and put a pull-up resistor on them. If I can’t do this, I need to add external parts to accomplish it.

Thanks.

Scott =)

kennethlimcp · May 16, 2015, 11:38pm

It might be possible with a change in this line:

github.com

particle-iot/firmware/blob/9b01d795ecaaf657399dc4888f30f3898d91d74a/src/spark_wiring_usartserial.cpp

/**
 ******************************************************************************
 * @file    spark_wiring_usartserial.cpp
 * @author  Satish Nair
 * @version V1.0.0
 * @date    13-March-2013
 * @brief   Wrapper for wiring hardware serial module
 ******************************************************************************
  Copyright (c) 2013 Spark Labs, Inc.  All rights reserved.
  Copyright (c) 2006 Nicholas Zambetti.  All right reserved.

  This library is free software; you can redistribute it and/or
  modify it under the terms of the GNU Lesser General Public
  License as published by the Free Software Foundation, either
  version 3 of the License, or (at your option) any later version.

  This library is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  Lesser General Public License for more details.

This file has been truncated. show original

But would have to be tested and verified. Maybe you can open an issue here: https://github.com/spark/firmware

prices · May 17, 2015, 1:11am

I will hack on that and test to see if it actually works for my application. If it does, then I will open a bug.

Thanks

prices · May 25, 2015, 6:31pm

This seems to work quite well. I have more testing to do, but it is working. However, my code won’t build for the Core in the develop branch. So I have to either wait until my Photons arrive, or until the Core is fixed in the develop branch to actually integrate this into the code and do a pull request.

prices · June 22, 2015, 4:41pm

Okay, I got my code compiling in the develop branch. It works significantly better than in the master branch. I also figured out that I could just enable half duplex mode on the serial port and it will do what I needed automatically. It even hooks the pins together internally.

I have a patch for that, but I am waiting for confirmation that how I did it is the best way to do it.

Thanks!