Datasheet

556
11011B–ATARM–21-Feb-12
SAM3N
556
11011B–ATARM–21-Feb-12
SAM3N
30.7.8.3 Local Loopback Mode
Local loopback mode connects the output of the transmitter directly to the input of the receiver,
as shown in Figure 30-32. The TXD and RXD pins are not used. The RXD pin has no effect on
the receiver and the TXD pin is continuously driven high, as in idle state.
Figure 30-32. Local Loopback Mode Configuration
30.7.8.4 Remote Loopback Mode
Remote loopback mode directly connects the RXD pin to the TXD pin, as shown in Figure 30-33.
The transmitter and the receiver are disabled and have no effect. This mode allows bit-by-bit
retransmission.
Figure 30-33. Remote Loopback Mode Configuration
30.7.9 Write Protection Registers
To prevent any single software error that may corrupt USART behavior, certain address spaces can be write-protected by
setting the WPEN bit in the USART Write Protect Mode Register (US_WPMR).
If a write access to the protected registers is detected, then the WPVS flag in the USART Write Protect Status Register
(US_WPSR) is set and the field WPVSRC indicates in which register the write access has been attempted.
The WPVS flag is reset by writing the USART Write Protect Mode Register (US_WPMR) with the appropriate access key,
WPKEY.
The protected registers are:
• “USART Mode Register”
• “USART Baud Rate Generator Register”
• “USART Receiver Time-out Register”
• “USART Transmitter Timeguard Register”
• “USART FI DI RATIO Register”
• “USART IrDA FILTER Register”
Receiver
Transmitter
RXD
TXD
1
Receiver
Transmitter
RXD
TXD
1