A doubt about USART and sleep mode?

Started by Bruce.J Sam July 26, 2004
   I have read the manual of PIC16F87X.In the section of "USART Synchronous Slave mode",it said "If enable bit TXIE is set, the interrupt will wake the chip from SLEEP and if the global interrupt is enabled,..." (Page.110)and "if enable bit RCIE bit is set, the interrupt generated will wake the chip from SLEEP."(Page.111).But in the section of asynchronous mode and synchronous master mode,the manual doesn't said the TXIE or RCIE if enable can wake the chip from SLEEP.Does only synchronous slave mode can use TXIE or RCIE to wake up from SLEEP?Why asynchronous mode and synchronous slave mode can't use them to wake?
       Thanks,
       Bruce .J Sam






   I have read the manual of PIC16F87X.In the section of "USART Synchronous Slave mode",it said "If enable bit TXIE is set, the interrupt will wake the chip from SLEEP and if the global interrupt is enabled,..." (Page.110)and "if enable bit RCIE bit is set, the interrupt generated will wake the chip from SLEEP."(Page.111).But in the section of asynchronous mode and synchronous master mode,the manual doesn't said the TXIE or RCIE if enable can wake the chip from SLEEP.Does only synchronous slave mode can use TXIE or RCIE to wake up from SLEEP?Why asynchronous mode and synchronous slave mode can't use them to wake?
       Thanks,
       Bruce .J Sam





I went through this a while ago so my memory is hazy on it but I
think its to avoid having the baud rate generator running during
sleep mode. So they didn't support Master Sync and Async. Slave
Sync draws its clock from the master so no BRG to run. Kind of a cop
out as I would have liked to have the option of running the BRG in
sleep mode. IIRC, the 18F series is much better on this front.

Phil

--- In , "Bruce.J Sam" <persevreman@y...>
wrote:
> I have read the manual of PIC16F87X.In the section of "USART
Synchronous Slave mode",it said "If enable bit TXIE is set, the
interrupt will wake the chip from SLEEP and if the global interrupt
is enabled,..." (Page.110)and "if enable bit RCIE bit is set, the
interrupt generated will wake the chip from SLEEP."(Page.111).But in
the section of asynchronous mode and synchronous master mode,the
manual doesn't said the TXIE or RCIE if enable can wake the chip from
SLEEP.Does only synchronous slave mode can use TXIE or RCIE to wake
up from SLEEP?Why asynchronous mode and synchronous slave mode can't
use them to wake?
> Thanks,
> Bruce .J Sam >
> ---------------------------------
>




Phil is right, the baud rate generator is shut down during sleep thus
it will only work in synchronous slave mode.

If you need this functionality you might look at chips that have
"nanoWatt" features as some, if not all, of them will have modes where
peripherals will continue to clock during sleep. If it is power
savings you are after you will save some but not at much as if you
went into a full sleep. For example the 18F2320 which I have been
working on recently will drop to about 40% of its normal current draw
when sleeping in the mode that continues to clock peripherals as
opposed to 1 or 2% of a full sleep.

I beleive there are 16F parts that support some nanoWatt features
though I'm not sure if they have these power management modes.

--Scott

, "Bruce.J Sam" <persevreman@y...> wrote:
> I have read the manual of PIC16F87X.In the section of "USART
Synchronous Slave mode",it said "If enable bit TXIE is set, the
interrupt will wake the chip from SLEEP and if the global interrupt is
enabled,..." (Page.110)and "if enable bit RCIE bit is set, the
interrupt generated will wake the chip from SLEEP."(Page.111).But in
the section of asynchronous mode and synchronous master mode,the
manual doesn't said the TXIE or RCIE if enable can wake the chip from
SLEEP.Does only synchronous slave mode can use TXIE or RCIE to wake up
from SLEEP?Why asynchronous mode and synchronous slave mode can't use
them to wake?
> Thanks,
> Bruce .J Sam