UART communication problem between ADuC845 and SiLabs controller.

I am trying to connect ADuC845 chip with a microcontroller from another vendor(Silicon labs-BGM13P22) via UART. I have set a baud rate of 115200 on both sides.

Configuration of ADuC845 that I have set is -->

CD = 0,DIV = 2,T3CON = 82H,T3FD = 2DH for 115200 baud rate

For BGM13P22 I have set:-->

115200 baud rate


1 Stop bit

no parity


the problem that I am facing is  BGM13P22 is able to transmit data to ADuC845 , ADuC845 is able to receive it, Now ADuC845 sends back some data to BGM13P22 . Now here BGM13P22 is not able to receive it, as control is not going inside receive interrupt handler of BGM13P22 .


Both microcontrollers have Vcc = 5V,I observed that voltage between tx and GND at ADuC845  = 3.3V and between RX and GND at BGM13P22 = 1.8V, Could this voltage drop be an issue?If yes,how can I solve it.


I will try to provide more detail, but for now can you suggest anything that I may be missing , any configuration settings for UART

is it the problem on BGM13P22 or ADuC845 ?


Any help is appreciated


Shikhar Tandon