Datasheet

WARNING
When the value of US_BRGR.FP is greater than '0', the SCK (oversampling clock) generates non-constant
duty cycles. The SCK high duration is increased by “selected clock” period from time to time. The duty
cycle depends on the value of USAR
T_BRGR.CD.
46.6.1.3 Baud Rate in Synchronous Mode or SPI Mode
If the USART is programmed to operate in Synchronous mode, the selected clock is divided by the value of
US_BRGR.CD.
BaudRate =
SelectedClock
CD
In Synchronous mode, if the external clock is selected (USCLKS = 3), the clock is provided directly by the signal on
the USAR
T SCK pin. No division is active. The value written in US_BRGR has no effect. The external clock
frequency must be at least 3 times lower than the system clock. In Master mode, Synchronous mode (USCLKS = 0
or 1, CLKO set to 1), the receive part limits the SCK maximum frequency to Selected Clock/3 in USART mode, or
Selected Clock/6 in SPI mode.
When either the external clock SCK or the internal clock divided (peripheral clock/DIV) is selected, the value of CD
must be even if the user has to ensure a 50:50 mark/space ratio on the SCK pin. When the peripheral clock is
selected, the baud rate generator ensures a 50:50 duty cycle on the SCK pin, even if the value of CD is odd.
46.6.1.4 Baud Rate in ISO 7816 Mode
The ISO7816 specification defines the bit rate with the following formula:
 =
Di
Fi
× 
where:
•
B is the bit rate
• Di is the bit-rate adjustment factor
• Fi is the clock frequency division factor
• f is the ISO7816 clock frequency (Hz)
Di is a binary value encoded on a 4-bit field, named DI, as represented in Table 46-3.
Table 46-3. Binary and Decimal Values for Di
DI field 0001 0010 0011 0100 0101 0110 1000 1001
Di (decimal) 1 2 4 8 16 32 12 20
Fi is a binary value encoded on a 4-bit field, named FI, as represented in T
able 46-4.
Table 46-4. Binary and Decimal Values for Fi
FI field 0000 0001 0010 0011 0100 0101 0110 1001 1010 1011 1100 1101
Fi (decimal) 372 372 558 744 1116 1488 1860 512 768 1024 1536 2048
Table 46-5 shows the resulting Fi/Di ratio, which is the ratio between the ISO7816 clock and the baud rate clock.
T
able 46-5. Possible Values for the Fi/Di Ratio
Fi/Di 372 558 744 1116 1488 1806 512 768 1024 1536 2048
1 372 558 744 1116 1488 1860 512 768 1024 1536 2048
2 186 279 372 558 744 930 256 384 512 768 1024
4 93 139.5 186 279 372 465 128 192 256 384 512
8 46.5 69.75 93 139.5 186 232.5 64 96 128 192 256
SAM E70/S70/V70/V71 Family
Universal Synchronous Asynchronous Receiver T
ransc...
© 2019 Microchip T
echnology Inc.
Datasheet
DS60001527D-page 1185