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OneWire library resets pinmode of pin 3 (Rx)


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I've been working on a project that uses both OneWire and Serial protocols. I realized that I could send serial data from the MSP430FR4133 launchpad to the computer and use the OneWire to read temperature data. I could not however send serial data from the computer to the launchpad when using OneWire. If OneWire was not used, serial data went both ways without a problem indicating an incompatibility between the OneWire and Serial libraries.

 

I tracked it down to a call to ds.reset() as the problem. Looking at the source for the OneWire.reset() function in OneWire.cpp, there was a suspicious call to pinMode and digitalWrite:

uint8_t OneWire::reset(void)
{
	pinMode(3, OUTPUT);  //why is this here?
	digitalWrite(3, HIGH);  //why is this here?
	IO_REG_TYPE mask = bitmask;
	volatile IO_REG_TYPE *reg IO_REG_ASM = baseReg;
	uint8_t r;
	uint8_t retries = 125;

Why was OneWire.reset() directly setting pin 3 (UART Rx) mode and value? Looking at Paul Stoffgren's site (http://www.pjrc.com/teensy/td_libs_OneWire.html), the suspicious lines were not there. I commented out the offending lines and now OneWire and Serial receive both work fine. I looked at the OneWire library for MSP432 and LM4F; they too have the same bug/feature. Did not check other architectures.

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