Data Sheet

437
Atmel | SMART SAM D21 [DATASHEET]
Atmel-42181G–SAM-D21_Datasheet–09/2015
The baud rate error is represented by the following formula:
Asynchronous Arithmetic Mode BAUD Value Selection
The formula given for f
BAUD
calculates the average frequency over 65,536 f
REF
cycles. Although the BAUD register can be
set to any value between 0 and 65,536, the values that will change the average frequency of f
BAUD
over a single frame
are more constrained. The BAUD register values that will affect the average frequency over a single frame lead to an
integer increase in the cycles per frame (CPF)
where
z D represent the data bits per frame
z S represent the sum of start and first stop bits, if present
Table 24-3 shows the BAUD register value versus baud frequency at a serial engine frequency of 48MHz. This assumes
a D value of 8 bits and an S value of 2 bits (10 bits, including start and stop bits).
Table 24-3. BAUD Register Value vs. Baud Frequency
⎟
⎠
⎞
⎜
⎝
⎛
−=
RateActualBaud
udRateExpectedBa
Error 1
)( SDCPF
f
f
BAUD
REF
+=
BAUD Register Value Serial Engine CPF f
BAUD
at 48MHz Serial Engine Frequency (f
REF
)
0 – 406 160 3MHz
407 – 808 161 2.981MHz
809 – 1205 162 2.963MHz
...
65206 31775 15.11kHz
65207 31871 15.06kHz
65208 31969 15.01kHz