AVR-Chat

hello guys,

i have a system that has 1 master microcontroller that communicates to 
18 slave microcontrollers. I am going to use a USART in UART mode. 
Since the master is using only one UART, there are control lines so 
that the communication b/n slave and master is one at time to avoid 
corruption. My question is that is this method reliable? When one 
slave controller transmit (toggling the lines high and low), hows does 
other slave controller affect the data? will they hold the line high? 
Any idea?

consulted mr google and seems rs485 is one solution. 

rgrds

mgu