Datasheet

723
SAM4S [DATASHEET]
11100E–ATARM–24-Jul-13
Figure 35-42.Local Loopback Mode Configuration
35.7.9.4 Remote Loopback Mode
Remote loopback mode directly connects the RXD pin to the TXD pin, as shown in Figure 35-43. The transmitter and the
receiver are disabled and have no effect. This mode allows bit-by-bit retransmission.
Figure 35-43.Remote Loopback Mode Configuration
35.7.10 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
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”
 “USART Manchester Configuration Register”
Receiver
Transmitter
RXD
TXD
1
Receiver
Transmitter
RXD
TXD
1