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Figure 33-3. 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 33-2 contains equations for the baud rate (in bits per second) and the BAUD register value for each
operating mode.
For asynchronous operation, there is one mode: arithmetic mode, the BAUD register value is 16 bits (0 to
65,535).fractional mode, the BAUD register value is 13 bits, while the fractional adjustment is 3 bits. In
this mode the BAUD setting must be greater than or equal to 1.
For synchronous operation, the BAUD register value is 8 bits (0 to 255).
Table 33-2. Baud Rate Equations
Operating Mode Condition Baud Rate (Bits Per Second) BAUD Register Value Calculation
Asynchronous
Arithmetic


16

=

16
1

65536
 = 65536 1 16


Asynchronous
Fractional


S

=

S  +

8
 =



8
Synchronous


2

=

2
 + 1
 =

2

1
S - Number of samples per bit, which can be 16, 8, or 3.
The Asynchronous Fractional option is used for auto-baud detection.
The baud rate error is represented by the following formula:
Error = 1
ExpectedBaudRate
ActualBaudRate
33.6.2.3.1 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)
 =


+
SAM D5x/E5x Family Data Sheet
SERCOM – Serial Communication Interface
© 2019 Microchip Technology Inc.
Datasheet
DS60001507E-page 918