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1745D–ATARM–04-Nov-05
AT91M55800A
18.1 Pin Description
Notes: 1. After a hardware reset, the USART clock is disabled by default. The user must configure the Power Management Controller
before any access to the User Interface of the USART.
2. After a hardware reset, the USART pins are deselected by default (see Section 16. ”PIO: Parallel I/O Controller” on page
112). The user must configure the PIO Controller before enabling the transmitter or receiver. If the user selects one of the
internal clocks, SCK can be configured as a PIO.
Table 18-1. USART Channel External Signals
Name Description
SCK
USART Serial clock can be configured as input or output:
SCK is configured as input if an External clock is selected (USCLKS[1] = 1)
SCK is driven as output if the External Clock is disabled (USCLKS[1] = 0) and Clock output is enabled (CLKO = 1)
TXD Transmit Serial Data is an output
RXD Receive Serial Data is an input