> auto baud rate detection

That's a possibility, although I did wonder about the
granularity/resolution of BRG

The OP's 24F datasheet is woefully shy on details, but
an 18F datasheet

http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=3Den547748

says -

16.2 Clock Accuracy with Asynchronous Operation

The factory calibrates the internal oscillator block
output (HFINTOSC). However, the HFINTOSC
frequency may drift as VDD or temperature changes,
and this directly affects the asynchronous baud rate.
Two methods may be used to adjust the baud rate
clock, but both require a reference clock source of
some kind

The first (preferred) method uses the OSCTUNE
register to adjust the HFINTOSC output. Adjusting the
value in the OSCTUNE register allows for fine
resolution changes to the system clock source. See
Section 2.6 "Internal Clock Modes" for more
information

The other method adjusts the value in the Baud Rate
Generator. This can be done automatically with the
Auto-Baud Detect feature (see Section 16.4.1 "Auto-
Baud Detect"). There may not be fine enough
resolution when adjusting the Baud Rate Generator to
compensate for a gradual change in the peripheral
clock frequency
--=20
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