I've been trying to use the Edison mini breakout board to communicate with my GPS module through the serial port (UART). My GPS module use RX/TX only and does not support RTS/CTS.
When I use the UART1, connect the J16 (USB) to computer and use Intel Arduino SDK to download and debug. The edison board is communicating to my GPS module correctly.
But after I unplug the USB cable from my computer, and use 3.6V Lithium battery to provide power, the edison module is not able to receive any data from my GPS module (I use the wifi to send out the number of data that the edison module received on the Serial Port. The GPS module is able to report data to my computer through serial port).
Then I use the 9V battery to plug in to the J21 port to supply the power (removed the 3.6V lithium battery). Now the edison module is able to receive data from my GPS module.
I noticed that on the last page of the "Intel Edison Breakout Board Hardware Guide", it indicates that there is a known error on all UARTs, and when sleep mode is enabled, a four-wire UART is required. I'm guessing when I use 3.6V lithium battery as power, it goes into sleep mode and requires RTS and CTS on the serial port. And when I use 9V battery to supply the power, the edison board does not go into sleep mode (just like plugging in the USB to the computer).
Anyone has any idea of how I can make this work? Thanks.