AT32UC3A3256S_2 Datasheet, PDF (545/1014 Pages) ATMEL Corporation – 32-bit AVR®Microcontroller

AT32UC3A3/A4
25.5 Product Dependencies
25.5.1 I/O Lines
The pins used for interfacing the USART may be multiplexed with the I/O Controller lines. The
programmer must first program the I/O 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 I/O 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. On USARTs not
equipped with the corresponding pins, the associated control bits and statuses have no effect on
the behavior of the USART.
25.5.2 Clocks
The clock for the USART bus interface (CLK_USART) is generated by the Power Manager. This
clock is enabled at reset, and can be disabled in the Power Manager. It is recommended to dis-
able the USART before disabling the clock, to avoid freezing the USART in an undefined state.
25.5.3 Interrupts
The USART interrupt request line is connected to the interrupt controller. Using the USART
interrupt requires the interrupt controller to be programmed first.
32072C–AVR32–2010/03
545