SAM7S256_14 Datasheet, PDF (363/775 Pages) ATMEL Corporation – ARM-based Flash MCU

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 pro-
gram 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 USART1 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 Man-
agement 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.
SAM7S Series [DATASHEET]
6175M–ATARM–26-Oct-12
363