Sounds like I2C to me.  8 bit transfers with a slave acknowledge at the end.
Implementing the master is a piece of cake, the slave is much harder but has
been done.  The scenix web site has slave code as one of it's virtual
peripherals, you might get some ideas from that.
http://www.scenix.com/virtual/vp/index.html

Regards

Mike Rigby-Jones


> -----Original Message-----
> From: John Esposito [SMTP:John_Esposito@DADEBEHRING.COM]
> Sent: Thursday, May 06, 1999 2:10 PM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      2-wire serial communication
>
> Hello all.
>
> I am trying to implement a 2-wire serial communication link between
> multiple PICs.  I will have one master, with several remote slaves.  The
> slaves will each have a keypad, an LCD display, and an auxiliary output -
> only 2 lines remain, one for the serial clock and serial data.
>
> I have been having difficulty developing a protocol for the communication
> -
> should the slaves poll the clock line or they be interrupted?  If
> interrupted, should they ACK before the master sends data?
>
> I would appreciate any help/guidance on this matter.
>
> Regards,
>
> --John