> From: Antonio Almeida <deec352@TOM.FE.UP.PT>
> To: PICLIST@MITVMA.MIT.EDU
> Subject: collision detection
> Date: Tuesday, 8 April 1997 23:25
>
> Hello,
>         I am building a PIC network and i pretend to use RS485 chips. I
> will use the built in UART to drive them but i need a way to detect
> collisions and network idle state, what i think i should do it's when i
> send a byte from the UART, or pretend to send it, i monitor the line with
> another pin (neither TX or RX) looking for diferent bits. Something link
> this:
>

If you used one of the manchester coded systems, you could use DC offset to
indicate collision. (note - this necessitates building your own serial data
stream with manchester bits in it - not too hard - there's some reasonable
comms books out there that indicate how.  I think ethernet uses a variant
of this.)

MikeS