UMTS & LTE EVB V2.2 board UART issue


I’m using the UMTS & LTE V2.2 EVB board with EG-91 module for a specific application development. In my setup, an STM MCU is being connected to the EVB board via RS232 interface (MAX3232) with hardware flow control enable. The MCU does not give any TX call-back interrupt when ever I send command to the modem.

The EVB uses SN6053238 for RS232 coms. Are these two (MAX3232 and SN6503238) compatible to each other?

Note: Both systems are tested on PC so no problem at all with the STM UART code or the EVB coms. It’s just the connection between these two that’s not working at all.

Any help would me much appreciated. Thanks


  1. MAX3232 and SN6503238 need to compare the corresponding data sheet
  2. If you want to use the hardware flow of the module, you need to use the AT command to open the hardware flow function of the module, you can first use the PC instead of the MCU to test the hardware flow control function of the module

The problem has been resolved. Both devices are talking to each other. I was using a self-made null modem cable were I forgot to short the DCD and DTR pins of the EVB modem side DB9 connector. As soon as I tied both pins together the communication started working.

Thanks by the way.