741
SAM4CP [DATASHEET]
43051E–ATPL–08/14
36.5.3 Interrupt
The USART interrupt line is connected on one of the internal sources of the Interrupt Controller. Using the USART
interrupt requires the Interrupt Controller to be programmed first.
36.6
Functional Description
36.6.1 Baud Rate Generator
The Baud Rate Generator provides the bit period clock, also named the Baud Rate Clock to both the receiver and the
transmitter.
The Baud Rate Generator clock source is selected by configuring the USCLKS field in the USART Mode Register
(US_MR) to one of the following:
The Peripheral clock.
A division of the Peripheral Clock, where the divider is product-dependent, but generally set to 8.
The external clock, available on the SCK pin.
The Baud Rate Generator is based upon a 16-bit divider, which is programmed with the CD field of the Baud Rate
Generator Register (US_BRGR). If a zero is written to CD, the Baud Rate Generator does not generate any clock. If a
one is written to CD, the divider is bypassed and becomes inactive.
If the external SCK clock is selected, the duration of the low and high levels of the signal provided on the SCK pin must
be longer than a Peripheral Clock period. The frequency of the signal provided on SCK must be at least 3 times lower
than the frequency provided on the Peripheral Clock in USART mode (field USART_MODE differs from 0xE or 0xF), or 6
times lower in SPI mode (field USART_MODE equals 0xE or 0xF).
Figure 36-2.
Baud Rate Generator
Table 36-3.
Peripheral IDs
Instance
ID
USART0
14
USART1
15
USART2
16
USART3
17
USART4
18
Peripheral Clock/DIV
16-bit Counter
0
Baud Rate
Clock
CD
CD
Sampling
Divider
0
1
>1
Sampling
Clock
Reserved
Peripheral Clock
SCK
(CLKO = 0)
USCLKS
OVER
SCK
(CLKO = 1)
SYNC
SYNC
USCLKS = 3
1
2
3
0
0
1
0
1
FIDI