Rs232

I want to connect to a PC (one serial port) 4 PLC's using a single serial BUS for all. I need to program this PLC's using the PC. I know that is possible because I saw but unfortunately I not notice the connection diagram. Was a serial bus using RS232 and the RS232 standard signals.
If exist somebody that have some knwledge about this please help.

I think you are asking for help even though you have posted this in the practice posting area.

First, what you have seen is probably some kind of bus network that is hooked up with the PC via an adapter.
This is certain, because RS232 only allows for one connection at a time. The adapter converts RS232 to the bus networks electrical level, which is probably RS485.

Second, there are many kinds of bus netwoks:
DH485, MPI, Profibus, Devicenet, CAN .. just to mention some of them.
If you could provide some more details we can help you better.
PLC type ?
Network type ?
Programming software ?
etc...

yes possible i used it to connect several pc together before rs485 was invented.
it uses a small relay at each plc.

Shooter, if you had relays switching the RS232 signals you were only talking to one device at a time, which is consistent with what JEsper said. I have, for testing purposes, had three devices simultaneously on a single RS-232 link, but it isn't reliable, and it isn't recommended. And only one was initiating communictions, the other two were just displays.