25.5.1 Baud Rate Generator

The baud rate generator provides the bit period clock named baud rate clock to both the receiver and the transmitter.

The baud rate clock is the peripheral clock divided by 16 times the clock divisor (CD) value written in the Baud Rate Generator register (DBGU_BRGR). If DBGU_BRGR is set to 0, the baud rate clock is disabled and the DBGU remains inactive. The maximum allowable baud rate is peripheral clock or GCLK divided by 16. The minimum allowable baud rate is peripheral clock divided by (16 x 65536). The clock source driving the baud rate generator (peripheral clock or GCLK) can be selected by writing the bit BRSRCCK in DBGU_MR.

If GCLK is selected, the baud rate is independent of the processor/bus clock. Thus the processor clock can be changed while DBGU is enabled. The processor clock frequency changes must be performed only by programming the field PRES in PMC_MCKR (see PMC section). Other methods to modify the processor/bus clock frequency (PLL multiplier, etc.) are forbidden when DBGU is enabled.

The peripheral clock frequency must be at least three times higher than GCLK.