Atmel Xplained Pro Evaluation Kit for the ATSAMD21J18A Microcontroller ATSAMD21-XPRO ATSAMD21-XPRO Data Sheet
Product codes
ATSAMD21-XPRO
424
Atmel | SMART SAM D21 [DATASHEET]
Atmel-42181C–SAM-D21_Datasheet–07/2014
Figure 24-3. Baud Rate Generator
contains equations for calculating the baud rate (in bits per second) and for calculating the BAUD register
value for each mode of operation.
For asynchronous operation there are two different modes. Using the arithmetic mode, the BAUD register value is 16 bits
(0 to 65,535). Using the fractional mode, the BAUD register is 13 bits, while the fractional adjustment is 3 bits. In this
mode the BAUD setting must be greater than or equal to 1.
(0 to 65,535). Using the fractional mode, the BAUD register 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 mode, the BAUD register value is 8 bits (0 to 255).
Table 24-2. Baud Rate Equations
S – Number of samples per bit. 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:
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
Operating Mode
Condition
Baud Rate (Bits Per Second)
BAUD Register Value Calculation
Asynchronous
Arithmetic
Arithmetic
Asynchronous
Fractional
Fractional
Synchronous
S
f
f
REF
BAUD
≤
)
536
,
65
/
1
(
BAUD
S
f
f
REF
BAUD
−
=
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
−
=
f
f
REF
BAUD
S
BAUD
1
536
,
65
S
f
f
REF
BAUD
≤
))
8
/
(
(
FP
BAUD
S
f
f
REF
BAUD
+
=
8
FP
S
BAUD
f
f
BAUD
REF
−
×
=
2
f
f
REF
BAUD
≤
)
1
(
2
+
=
BAUD
f
f
REF
BAUD
1
2
−
=
f
f
BAUD
REF
BAUD