UART itnerface doesn't work with external power supply

[pmrlcbtcphtzjdq]

Hallo!
I'm having issues with my second UART interface in MPC5748G  in the dev-kit board - it doesn't work when I switch to the external voltage of 12V.

In my application I'm using two PAL instances of UART - one, the pal1 is connected with the microUSB cable, and it works for both sources of power.

However, the second UART interface, pal2, connected to PA5 and PA6 pins, works only when using the 5V power over the microUSB. When I switch to external power of 12V the UART connection doesn't work, although other parts of the application work fine.

Does anybody have any suggestions why this happens?

[lukaszadrapa]

Hi,

I can't see reason for this. Did you check TX pin by an oscilloscope? Do you use RS232 or similar voltage level translator? If yes, how is it supplied?

Regards,

Lukas