Data Sheet

436
Atmel | SMART SAM D21 [DATASHEET]
Atmel-42181G–SAM-D21_Datasheet–09/2015
Figure 24-3. Baud Rate Generator
Table 24-2 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.
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.
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
Asynchronous
Fractional
Synchronous
S
f
f
REF
BAUD
≤
)536,65/1( BAUD
S
f
f
REF
BAUD
−=
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
−=
f
f
REF
BAUD
SBAUD 1536,65
S
f
f
REF
BAUD
≤
))8/(( FPBAUDS
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