Rabbit 3000, User Manual

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User’s Manual 147
The clock input to the serial port unit must be 8 or 16 (selectable) times the baud rate in the
asynchronous mode and 2 times the baud rate for the clocked serial mode when the internal
clock is used. Timers A2–A7 supply the input clock for Serial Ports A–F. These timers can
divide the frequency by any number from 1 to 256 (see Chapter 11). The input frequency to
the timers can be selected in different ways described in the documentation for the timers.
One choice is the peripheral clock—with that choice and a well-chosen crystal frequency
for the main oscillator, the most commonly used baud rates can be obtained down to
approximately 2400 bps or lower by prescaling timer A0 at the highest Rabbit clock fre-
quencies (see Section A.4 in Appendix A).