Datasheet

Figure 25-3. Baud Rate Generator
Base
Period
Selectable
Internal Clk
(GCLK)
Ext Clk
CTRLA.MODE[0]
0
1
0
1
0
1
0
1
f
ref
Clock
Recovery
Tx Clk
Rx Clk
CTRLA.MODE
/2 /8
/1 /2 /16
Baud Rate Generator
Table 25-2 contains equations for the baud rate (in bits per second) and the BAUD register value for each
operating mode.
For asynchronous operation, the BAUD register value is 16 bits (0 to 65,535).
For synchronous operation, the BAUD register value is 8 bits (0 to 255).
Table 25-2. Baud Rate Equations
Operating Mode Condition Baud Rate (Bits Per Second) BAUD Register Value Calculation
Asynchronous
Arithmetic





16


=


16
1 

65536
 = 65536  1  16 




Synchronous





2


=


2 
 + 1
 =


2  

 1
The baud rate error is represented by the following formula:
Error = 1 
ExpectedBaudRate
ActualBaudRate
25.6.2.3.1 Asynchronous Arithmetic Mode BAUD Value Selection
The formula given for f
BAUD
calculates the average frequency over 65536 f
ref
cycles. Although the BAUD
register can be set to any value between 0 and 65536, the actual average frequency of f
BAUD
over a
single frame is more granular. 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
• D represent the data bits per frame
• S represent the sum of start and first stop bits, if present.
Table 25-3 shows the BAUD register value versus baud frequency f
BAUD
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).
SAM D21 Family
SERCOM – Serial Communication Interface
© 2018 Microchip Technology Inc.
Datasheet Complete
DS40001882D-page 464