Datasheet

...........continued
D
(Data bits+Parity)
R
SLOW
[%] R
FAST
[%] Max. total error [%] Recommended max. Rx error [%]
9 96.39 104.76 +3.61/-4.76 ±1.5
10 96.70 104.35 +3.30/-4.35 ±1.5
The following equations calculate the ratio of the incoming data rate and internal receiver baud rate:

SLOW
=
 + 1 
  1 +    + 

,

FAST
=
 + 2 
 + 1  + 

• R
SLOW
is the ratio of the slowest incoming data rate that can be accepted in relation to the receiver
baud rate
• R
FAST
is the ratio of the fastest incoming data rate that can be accepted in relation to the receiver
baud rate
• D is the sum of character size and parity size (D = 5 to 10 bits)
• S is the number of samples per bit (S = 16, 8 or 3)
• S
F
is the first sample number used for majority voting (S
F
= 7, 3, or 2) when CTRLA.SAMPA=0.
• S
M
is the middle sample number used for majority voting (S
M
= 8, 4, or 2) when CTRLA.SAMPA=0.
The recommended maximum Rx Error assumes that the receiver and transmitter equally divide the
maximum total error. Its connection to the SERCOM Receiver error acceptance is depicted in this figure:
Figure 26-5. USART Rx Error Calculation
+
+
Error Max (%)
Error Min (%)
Baud Rate
SERCOM Receiver error acceptance
from RSLOW and RFAST formulas
Baud Generator offset error
depends on BAUD register value
+
Clock source error
Recommended max. Rx Error (%)
The recommendation values in the table above accommodate errors of the clock source and the baud
generator. The following figure gives an example for a baud rate of 3Mbps:
Figure 26-6. USART Rx Error Calculation Example
+
+
Error Max 3.3%
Error Min -4.35%
Baud Rate 3Mbps
SERCOM Receiver error acceptance
sampling = x16
data bits = 10
parity = 0
start bit = stop bit = 1
No baud generator offset error
Fbaud(3Mbps) = 48MHz *1(BAUD=0) /16
+
DFLL source at 3MHz
+/-0.3%
Recommended
max. Rx Error +/-1.5%
(example)
Error Max 3.3%
Error Min -4.35%
+
Error Max 3.0%
Error Min -4.05%
Transmitter Error*
Accepted
Receiver Error
security margin
*Transmitter Error depends on the external transmitter used in the application.
It is advised that it is within the Recommended max. Rx Error (+/-1.5% in this example).
Larger Transmitter Errors are acceptable but must lie within the Accepted Receiver Error.
SAM D21 Family
SERCOM USART
© 2018 Microchip Technology Inc.
Datasheet Complete
DS40001882D-page 476