Hi Muhammad,

real multimaster are CAN or I2C, which need special interface chips or already build in in some 8051 derivates.
E.g. C505 with CAN,
80C652 with I2C.


The standard UART have no collision detection. So it can only be used in single master applications.

To avoid collisions, there are several ways, following 2 easy methods:

1.
The master polls every slave (easiest way).
This can be done with RS232 or RS485 drivers, which can be deactivated. So always only 1 active transmitter on the line.
Also current loop or CAN driver can be used without needing deactivate the transmitters.


2.
Every slave, which want to tell something, send a break. A break was all bits 0 including the stop bit. So a break from a 2. second slave or beginning a master transmission can not change it (0 level = dominant).
Then after this the master can address all slaves to detect one, which sent the break.
But this need also special busses, which allow 2 active transmitter on the same time with the low level was dominant, e.g. current loop or CAN drivers.
RS232 or RS485 can not do it !.


Peter