Jeff Cesnik wrote:
>
> Does anyone have an example schematic (or know where to find one) using
> two PIC16F84's communicating over an RS-422/485 link?  I've done RS-232,
> but have absolutely no experience with balanced line communications.
> Can someone recommend a good line driver/receiver suitable for
> interfacing with the PIC?
>
> -Thanks

Hi,

   If you've got the code for RS-232 you should have very little trouble
implementing RS-485 or RS-422.

I've not used RS-422, so I'll restrict my comments to RS-485. I used the
MAX485 but there are a whole range or transcievers which fit the same
package. 8-pin PDIP and pretty cheap.

The only thing you have to remember it that you need to include
terminators at either end of the network (if you only have two nodes
it's one each). You will probably also want to add a pair of resistors
to bias the lines so that noise doesn't trigger the receive routines. I
found a neat summary of this on http://www.bb-elec.com/techlibr.html

I went for a two wire interface, data, and transmit/receive. The
bit-banged 9600 baud comms.

To send, a PIC checks that the line is inactive, then enables the
transmit and sends it's serial data. By using PB0 as the data pin I was
able to use the interrupt to trigger the receive routine. The routines
used are pretty much the same as for RS-232.

Hope this is some help,

Keith.