Microchip Technology MA160014 Data Sheet
PIC18(L)F2X/4XK22
DS41412F-page 276
2010-2012 Microchip Technology Inc.
16.2
Clock Accuracy with
Asynchronous Operation
Asynchronous Operation
The factory calibrates the internal oscillator block
output (HFINTOSC). However, the HFINTOSC
frequency may drift as V
output (HFINTOSC). However, the HFINTOSC
frequency may drift as V
DD
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.
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
register to adjust the HFINTOSC output. Adjusting the
value in the OSCTUNE register allows for fine
resolution changes to the system clock source. See
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
Generator. This can be done automatically with the
Auto-Baud Detect feature (see
). There may not be fine enough
resolution when adjusting the Baud Rate Generator to
compensate for a gradual change in the peripheral
clock frequency.
compensate for a gradual change in the peripheral
clock frequency.