Fastrack FXT009 - Problem with GPIO (in)


Hi all
Greetings from Mexico :smiley:

I’m currently developing an application that connects the Fastrack with a device in order to get and set information from and to it. The way I use the fastrack is connecting the serial port with the device for information exchange. (I only use 3 pins -read RXD, write TDX, ground GND), and the db15 cable (converted to db9) to a laptop in order to read the commands in the ‘HyperTerminal’ software.

When I use the DB15 cable plugged to a laptop, the GPIO pin reads values of 1 and 0 (5 volts and 0 volts) correctly, the GPIO-Input pin being the #25.

The problem comes when I disconnect the DB15 cable and let the device work unmonitored, when I do that, the GPIO-In pin always reads 1, always, no matter if I put 5V or 0V.

Seems to me that this is an electronic problem, but I have no idea why or how to solve it.
Any help would be appreciated, this is the only detail keeping me from doing pilot tests.

Thanks in advance.



Have you had a close read of the FXT Series User Guide, section

My reading of it is that unless you have configured the Vref (Pin 3) for the appropriate input voltage range, the max input to these pins is configured to be between 2V3 - 2V6.

A couple of notes to be aware of:


The other thing that comes to mind is that I recall that the GPIO have to be set up after a power cycle or reset. Are you resetting the modem after removing the HD15?

I know it’s probably a dumb thing to ask - but how are you checking the state of the GPIO pins when you have the comms from the PC removed? If you’ve got an expansion card with USB, try connecting via USB and watching the state of the GPIO via the AT+WIOR command.

Hope this helps.

ciao, Dave