4 serial inputs 1 chip

[Archangel]

I am beginning a new project. I want to connect 4 Parallax RFID readers to a PIC 16F877.
I have already have the code written for one reader, but now I need to expand to 4. I know I will need to use ports other than only the internal USART.

Do you have a spare MCU pin on the reader's pics? If so you could hook the readers all to the usart with a series resistor on each, then when a reader sends data it could pull that spare pin low which signals the other readers to standby, (all spare pins hooked together). Just make sure the reader's output pins Idle in the High state.