AT32UC3A3256S_1 Datasheet, PDF (534/961 Pages) ATMEL Corporation – AVR32 32-Bit Microcontroller

AT32UC3A3
26.6 Product Dependencies
26.6.1 I/O Lines
The pins used for interfacing the USART may be multiplexed with the PIO lines. The program-
mer 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. On USARTs not
equipped with the corresponding pins, the associated control bits and statuses have no effect on
the behavior of the USART.
26.6.2 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.
26.6.3 Interrupts
The USART interrupt line is connected on one of the internal sources of the Advanced Interrupt
Controller. Using the USART interrupt requires the INTC to be programmed first. Note that it is
not recommended to use the USART interrupt line in edge sensitive mode.
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