----------
> I'm running a little tight on PIC I/O pins, namely I have three lines
> available. I would like to tie a Dallas DS1302 RTC and Philips 8570
serial
> RAM onto these three lines.
>
> My question deals with possible protocol collisions with these two
devices.
> It's easy to not select the RTC with RST line when talking to the RAM.
> However the reverse is not true. Do you think talking to the RTC with its
> protocol on B1 and B2 could inadvertantly issue legitimate commands to
the
> RAM?
>
> craig

Things to consider:

Many I2C devices do not have a reset line which would assure proper initial
conditions.  These devices often depend on a "power up" to reset to initial
conditions. It is prudent to issue a sequence of signals which would
effectively abort any ongoing commands.  This is important in embedded
systems which may be reset without going through a "power up".  An I2C buss
will not work properly as a shared resource!  Care must be taken in a
multitasking system to allow one and only one task to control the buss.  A
common pitfall is to attempt to control the buss in foreground and also
allow access by an ISR.

The Phillips data book titled "I2C Peripherals for Microcontrollers", 1992
is an excellent reference.  I may be able to find code which issues the
sequence of signals needed to resync the devices if your interested.

Thanks,
Jimmie

        Jim Curry and Associates
        13339 N. Central Expy.
        Dallas, TX 75243
        Voice:    214 680-1540
        Fax:      214 680-1562
        Email:    jcurry@airmail.net
        Web Page: http://web2.airmail.net/jcurry/