Hi all,

I have a system made up of two 16F PIC-based devices and connected by =20
I2C.  One is a bit-banged master (called M here) and the other a =20
MSSP-based slave (called S here).  S reads A/D data repeatedly and =20
controls other things, and M requests specific data from S repeatedly =20
and displays it (on M).  M also controls other parameters in S =20
occasionally.

I need to add another device in this system as an additional display =20
(retrieve data from S repeatedly and display it), but trying to figure =20
out the best way to do this.  It will have to be bit-banged.  Let's =20
call it N.  Here are the options I've come up with...

(1) N is also a slave.  M asks N what it wants to display, requests it =20
from S and sends it to N.  Pro =3D simplicity.  Con =3D lots of I2C =20
traffic, and M has a lot more work to do.  M is already quite busy =20
with it's own I2C bit-banging.

(2) N is a second master, and asks S directly for what it wants and S =20
sends it directly to N.  M is not involved (nice), but I'd have to =20
modify N's code to support multi-master.  So far (reading the Philips =20
I2C spec) it seems like the multi-master arbitration is not trivial, =20
and I'm concerned if M has any more processing capacity for this.  Pro =20
=3D less I2C traffic.  Con =3D complicated.  Think option 1 is still =20
better here, and I'd just speed up the I2C data.

(3) Not sure if this option is possible, but here N is a slave.  M =20
asks it what it wants, and tells S, who sends it directly to S (on the =20
same I2C bus).  Here, S would have to change to being a master =20
temporarily, but I'd also have to tell M to shut up for a bit.  =20
Haven't quite figured out how to do this yet, other than with M =20
knowing this, it can stay quiet for a given time.  But that may not be =20
reliable.

(4) Here too, as in 3 above, S would send the result directly to N, =20
but it would broadcast (multicast) the result, which N will see and =20
use (M would ignore).  It this even possible?  Or would S have to be a =20
master temporarily anyway to broadcast the data?

Thoughts?  Better ideas?

Cheers,
-Neil.




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