[BC660K-GL] Is the VIO_SEL - GND connection essential for 3.3 V operation?

Hello all :slight_smile:

I have a MCU which runs at 3.3 V, and have interfaced that with a BC660K-GL through the main UART port. Due to prototyping reasons the VIO_SEL pin was unfortunately not connected to GND as was specified in the design guide (it’s at the bottom of the chip, therefore difficult to solder). Also, the 1 kOhm resistors were left out as well.

Now the problem is that my main MCU is not able to communicate with the BC660K, even though all the other connections are as they should be (as far as I can tell). So the question is, could the reason for the problem be that VIO_SEL is not connected to GND (or the missing resistors)? Or should it be able to function nonetheless?

Any feedback is much appreciated!

N.B. With the BC66 I managed to interface it to a 3.3 MCU with the main UART port, without any level conversion and then went fine (even though the hardware design guide advises to use level conversion). So I was hoping that for the BC660K-GL the same applies.

@herbert.pan-Q , any ideas? :slight_smile:

I think we can check by the following methods
1、First, just test whether main_tx/rx of the module is communicating properly
2、Determines whether the baud rates of the mcu match