Ok, let's try something easy:

Two Chip Select ( CS ) signals are required to select F84ONE or F84TWO.
Both F84 have Tx data connected together and tied to RX pin on F877.
When CS is low ( as an example ) the specific TX become output. A CS high
means a TX line as input. So only one F84TX could be output once.
( you may use only one CS and two different logic levels for selected chip
ie: f84ONE is selected for CS high and f84TWO for CS low but one of two
chips must send bytes all the time )
When one F84 is selected will transmit asynchronously the keypad data at
desired baud rate. Keypad data must be buffered so will be no
transmission error when the user is pressing buttons; the last data is
send.
 Slaves must have software asynchronous routines ( if PIC16F84 is used )
and master can receive using hardware USART.
You'll need the same USART software if you switch from f84 to f62x.
Slaves will have implemented only transmision routine and master
only receiving routine.
You may found all these routines by searching  in the IO section at
piclist.

best, Vasile


On Tue, 19 Mar 2002, T Vavouras wrote:

> Thank you for your reply!
> What I seem to have forgotten to mention in my original message was that I
> am a newbie who has bitten a graduate project involving PICs which I'm
> finding difficult to chew!  In other     words... I'm not quite sure i know
> how to implement (see program) your suggestion! Any directions, or where I
> could find anything similar in assembly?
>
> Many thanks in advance,
> Theodore
>
> ----- Original Message -----
> From: "Vasile Surducan" <vasile@S3.ITIM-CJ.RO>
> To: <PICLIST@mitvma.mit.edu>
> Sent: Tuesday, March 19, 2002 10:20 AM
> Subject: Re: [PIC]: Communicating between 16F84 and 16F877
>
>
> > My mind is resting on SPI.
> >
> > I'll try something similar, with clk, data and two chip
> > select.
> > The master will send a clk to the chip selected. The slave will respond
> > with 8 bit of data ( or more ) on any rising or falling clock edge. On the
> > same bus only selected chip will answer. For small distances up to 2.5...3
> > meters no level converters are required if twisted wires are used (
> > clk/gnd, data/gnd, cs/gnd )
> >
> > best, Vasile
> >
> > P.S. From the tea rebellion at Boston, half of the world is speacking a
> > different english... so spelling correctly is like Einstein relativity
> > theorem...
> >
> >
> >
> > On Tue, 19 Mar 2002, T Vavouras wrote:
> >
> > > I have two 16F84 ('slaves') each reading an 8button keypad.
> >  I configure portb of each PIC to read the input.
> > I need to send the 8bit input state to a 'master' (probably a 16F877)
> > once there is a change (a button is pressed or released).
> >  Can i do it just using an RX and a TX line? how?
> >  if not possible, what else do you suggest?
> > > many thanks
> > >
> > > --
> > > http://www.piclist.com hint: The list server can filter out subtopics
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> > >
> > >
> >
> > --
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> >
> >
>
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>

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