serial communication (master and slave)

[red]

Hi I am using 3 microcontrollers for serial communication. 1 as master and remaining are slaves. communication work fine (slave response to the Master's Poll) but if i add another one, that all of the slave don't respond anymore to the master's POLL. The hardware setup is that the master TX is connected to the slave's RX and vice versa (sort of UART bus). If I remove the common ground connection for the slave 3 and master, the 2 other slave can now respond to the master's POLL, also the slave 3 can recieve Poll but can't reply back. I appreciate any help. tnx

[Ttelmah]

Er.
How is the wiring going to work with 3 chips?.
You will end up with two slave TX lines connected to one master RX, which means that two driver devices are talking to the same line... :-(
This is almost certainly what is happening, preventing the third chip from driving the line. When you disconnect the ground, there is no longer a complete 'circuit', so the short disappears.
You need to disconnect the drivers, when you are not actually operating the line. Now, the compiler has an option for this (output_float), but I'd suspect this will only work with the software UART (you'd need to check).

Best Wishes