Hi all,
As per my schematic below and my breadboard set up I’m already executing serial communications successfully between the PIC18F2580 and the ETRX357HR Zigbee module but I’m being advised by my board house there is the potential for serial communication issues to arise due to the differing voltages powering the PIC18F2580 and the ETRX357HR Zigbee module.
Here's my schematic:
Their advice is based on the absolute maximum ratings of the Zigbee module whereby in the Zigbee module manual it is stated:
Absolute Maximum Ratings:
Inputs: -0.3V to Vcc + 0.3V
Essentially this means the voltage on any input pin should not be above 3.6V in this design, since it is being powered from 3.3V. This is violated on Pin 17, in the PIC18F2580 Tx to Zigbee module Rx. Having looked around for a solution I believe I can improve the situation by adding something like a 10k resistor.
This will limit the current that will flow through the Zigbee module's input pin protection diode, but since a max current rating for it is not given, you just have to guess at the resistor value.
Does anyone see a problem with having a 10k resistor between the serial communications lines? If so any ideas for a better solution?
Here are the respective datasheets:
Zigbee module -
**broken link removed**
PIC18F2580 -
http://ww1.microchip.com/downloads/en/DeviceDoc/39637b.pdf
Thanks,
TokTok.