Hello,

I want to interface SDI-12 device to 89c52 microcontroller.
My device will be SDI-12 slave.
1) SDI-12 protocol is normal asynchronous ASCII protocol with fix 1200 baud
with 1 start bit, 7 data bits ,1 parity and one stop bit.

2) As in SDI-12 protocol before sending command master has to keep bus high for minimum 12ms (Break signal )and then low for minimum 8.33ms (mark signal ).

3) when SDI-12 slave (my device)device sends response It has to keep bus low (mark signal)for 8.33ms before sending response

For above requirement can I use UART of 89c52 ? How to monitor bus low or High for few millisecond when I am not in port pin mode working with UART?
How to keep bus Low and High in UART mode?

one option that I can see is poll port pin first and then put it into UART mode if I get correct time sequence of low and high while receiving command .

and at the time of response first keep low signal using port pin and then send a byte in UART mode?

Can any one suggest me How should I use UART in above case?