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:

 +CFUN: 1

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


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.

i have the same issue with BG77
the MAIN UART have no response
what could be the problem
is this the same problem as MG77xA-GL and need to pull high the PON_TRIG?

I think not, BG77 has no similar limition, are you using EVB+TE-A kit or custom device?

the board is connected to the network and it’s working.
UART has been connected to usb to ttl 5v module directly but no response form the module after sending AT commands and when i reset the board it sends some none sense characters except that i get nothing from the module
i guess that it’s because of the voltage level difference but i had another EC200 module that was working with the same design.


is this relevant to my problem?
board is on and the net status LED is blinking

yes, the module volatge is 1.8V, so you need to convert to 1.8V instend of connect to 5V directly.

ok let me try that
also would you do me another favor
i need the driver of EC200A for raspbian OS or linux
can you send them?

Yes, please check follow link:


I have encountered similiar issue with MAIN UART reception. In our design we have PON_TRIG pin pulled high to 1.8V from external MCU. Power up sequence is the same as described in “hardware design” note. Still, modem in not responding for any AT commands, although I can see initial messages like:
+CFUN: 1

Do I have to connect DBG UART as commented above?

Hi @aluczak

Yes, you need connect UART_DBG and pull up PON_TRIG to high.