Stephen D. Barnes wrote:
> According to the datasheet for the 18F4320 (DS39599B) the internal
> oscillator runs at 8MHz.

+/- the precision of the INTOSC, of course, and verify that you don't
use the INTOSC postscaler...

> If I am correct, the datasheet tells me that the internal oscillator is not
> divided by 4 in the way an external timing source would be (crystal, clock,
> resonator...applied to OSC1 and OSC2 pins).

None of the possible clock sources are devided by 4, as far as I know.

*But*, the "instruction cycle" time is Fosc/4 (or
rather the invers of Fosc/4) no matter the source of
Fosc (xtal, external clock, INTOSC...) but that's
not directly related to the baud rate generator calculation.).

Where does in say the that clock is divided by 4 ?

> For USART configuration, should
> I use a value of 32MHz

No. 8 Mhz.

> I am having problems with USART communications...it
> does not work

In what way ?

> and I believe the problem may be that I have done the baud
> rate calculation using the 8MHz INTOSC value as FOSC in the
> equation above.

Shouldn't be that.

> Am I on the right track?

Yes.

20 Mhz xtal  -> use 20 Mhz in UART formulas.
8 Mhz INTOSC -> use 8 Mhz in UART formulas.

If you "feed" the PIC with an external clock,
use the freq of that clock in UART formulas.

So there is no divide by 4 in either case.

To verify your UART settings, you could always connect
a xtal (and reconfigure the CONFIG settings) to get a
know/better Fosc precision and verify your UART settings
from that.

Jan-Erik.

--
http://www.piclist.com hint: To leave the PICList
mailto:piclist-unsubscribe-request@mitvma.mit.edu