Atmel Evaluation Kit AT91SAM9G25-EK AT91SAM9G25-EK Data Sheet

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SAM9G25 [DATASHEET]

11032D–ATARM–10-Mar-2014

The pins used for interfacing the USART may be multiplexed with the PIO lines. The programmer must first program the 
PIO controller to assign the desired USART pins to their peripheral function. If I/O lines of the USART are not used by the 
application, they can be used for other purposes by the PIO Controller.

To prevent the TXD line from falling when the USART is disabled, the use of an internal pull up is mandatory. If the 
hardware handshaking feature is used, the internal pull up on TXD must also be enabled.

The USART is not continuously clocked. The programmer must first enable the USART Clock in the Power Management 
Controller (PMC) before using the USART. However, if the application does not require USART operations, the USART 
clock can be stopped when not needed and be restarted later. In this case, the USART will resume its operations where 
it left off. 

Configuring the USART does not require the USART clock to be enabled. 

USART0

CTS0

PA3

A

USART0

RTS0

PA2

A

USART0

RXD0

PA1

A

USART0

SCK0

PA4

A

USART0

TXD0

PA0

A

USART1

CTS1

PC28

C

USART1

RTS1

PC27

C

USART1

RXD1

PA6

A

USART1

SCK1

PC29

C

USART1

TXD1

PA5

A

USART2

CTS2

PB1

B

USART2

RTS2

PB0

B

USART2

RXD2

PA8

A

USART2

SCK2

PB2

B

USART2

TXD2

PA7

A

USART3

CTS3

PC25

B

USART3

RTS3

PC24

B

USART3

RXD3

PC23

B

USART3

SCK3

PC26

B

USART3

TXD3

PC22

B