>   What I am wondering is this - I have a 16c773 sleeping, and I have
> asynchronous USART communications only. Soon I will have set up the I2C.
It
> looks like only the I2C will be able to wake it up. (I don't think I can
> just flick over to syncronous USART befor issuing sleep). Does anyone have
> experience with this and could give more details on how to set it up for
> wake up using I2C, or have some code?

I haven't looked into the details of this, but it makes sense.  The UART
baud clock is derived from the main processor clock, which is shut off
during sleep, which explains why it can't be looking for a start bit during
sleep.  This also explains why it can wake up from sleep in synchronous mode
since no baud clock is required for reception.

You could tie the RX line to a different interrupt that can wake up from
sleep.  You will still loose at least the first character and probably much
more depending on startup timer, oscillator type, and transmission speed.
However, this may be fine if the protocol is designed with this in mind.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, olin@embedinc.com, http://www.embedinc.com

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