I have read few articles none of them helped on topic how to resolve issue with UART.
I made PCB (via JLCPCB) that has STM and SIM7080G controllers. I had logic level shifter making 3.3V to 1.8V but it didnt work. Then I desoldered logic level shifter and replaced it with screenshot below transistors / voltage divider.
After connecting I measured all levels. Like before 1.8V on SIM levels and 3.3V on connection to my USB-TTL. Basically I think my UART is fried or I have to reflash SIM firmware. Currently I do not own osciloscope to check edges But I will purchase if I have to.
Any ideas that might help? Tried baudrate 115200 or 9600.