Atmel SAM4S Series, Preliminary Data Sheet

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767
11100B–ATARM–31-Jul-12
SAM4S Series [Preliminary]
Figure 34-42. Local Loopback Mode Configuration
34.7.9.4 Remote Loopback Mode
Remote loopback mode directly connects the RXD pin to the TXD pin, as shown in Figure 34-43 .
The transmitter and the receiver are disabled and have no effect. This mode allows bit-by-bit
retransmission.
Figure 34-43. Remote Loopback Mode Configuration
34.7.10 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 automatically reset by reading the USART Write Protect Mode Register (US_WPMR) with the appropri-
ate 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”
• “USART Manchester Configuration Register”
Receiver
Transmitter
RXD
TXD
1
Receiver
Transmitter
RXD
TXD
1