BG770A TE-A module: UART Main rx

We have just received a few BG770A-GL TE-A modules. With our existing UMTS/LTE-EVB-KIT, we are unable to send any characters to the module via UART (MAIN). When we turn on the module, we do see TX data:

 RDY
 +CFUN: 1
 +CPIN: NOT INSERTED
 APP RDY

However, we cannot type any AT commands at this point, as if the RX signal is not hooked up. We can replace the BG770A module with a BG96/95, and that works perfectly fine to send commands, so I have verified the USB/Serial cable is OK.

Is there something special on this module that needs to be set? Have tried different flow control settings, and state of the PON_TRIG switch on the BG770A TE-A

Hi,

For BG77xA-GL series module, you need push PON_TRIG to High and UART_DBG must connect USB cabel,then we can send AT command via MAIN UART.

I have been able to talk via MAIN UART, but only after attaching UART_DBG, as you mentioned.

I am confused on this behavior. Why does the UART_DBG need to be attached in order for us to use primary AT commands on the MAIN UART? What does this mean for production?

Hi Cblack,

For BG77xA-GL or BG95xA-GL series module, the comminication of MAIN UART controled by PON_TRIG pin, only in High posistion AT commands can be sent, and PON_TRIG need
supply by USB cable( PON_TRIG needs to be pulled high electricity level externally). this is mandatory.