Datasheet

 2017 Microchip Technology Inc. DS60001516A-page 447
SAM9G20
31.5 Product Dependencies
31.5.1 I/O Lines
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 or Modem mode is used, the internal pull up on TXD must also be enabled.
All the pins of the modems may or may not be implemented on the USART. Only USART0 is fully equipped with all the modem signals.
On USARTs not equipped with the corresponding pin, the associated control bits and statuses have no effect on the behavior of the
USART.
31.5.2 Power Management
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.
31.5.3 Interrupt
The USART interrupt line is connected on one of the internal sources of the Advanced Interrupt Controller. Using the USART interrupt
requires the AIC to be programmed first. Note that it is not recommended to use the USART interrupt line in edge sensitive mode.