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Connecting an XBee reset line to a microcontroller

Due to the fact that many Digi RF products require the Reset line to be pulled low as an open collector, we suggest to never drive the reset line high for cross compatibility.  Some of the microprocessors in the XBEE product line pull the reset line low for a few milliseconds after a reset occurs.  You can directly connect the reset line to an external microcontroller using a pull-up resistor and toggling the processor pin as output low or input/HighZ in order to control the line.  If there is concern that someone might mistakenly set the drive of the processor high, a 200 OHM resistor should be placed between the two devices to ensure a dead short does not occur while the XBEE pulls the reset line low.
 
The XBEE should have its own dedicated reset line if a reset on the XBEE would reset other devices.  The reset line should be kept as short as possible to keep noise off of the line.  We recommend a 10nF to 100nF cap should be added to ground if the line is longer than 2cm of microstrip, or if in a noisy environment to prevent accidental resets.  It is best to run the reset line by stripline to reduce external and local noise as well as RF transmissions.
 
The second option is to use a transistor/mosfet as open collector/drain on the reset line.  Many of the other noise preventative measures apply to both the input of the transistor/mosfet as well as the collector/drain side.
Last updated: Aug 23, 2017

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