Datasheet

SAM9261 [DATASHEET]
Atmel-6062O-ATARM-SAM9261-Datasheet_21-Jun-16
454
Figure 31-27. Example of RTS Drive with Timeguard
31.6.7 Test Modes
The USART can be programmed to operate in three different test modes. The internal loopback capability allows
on-board diagnostics. In the loopback mode the USART interface pins are disconnected or not and reconfigured
for loopback internally or externally.
31.6.7.1 Normal Mode
Normal mode connects the RXD pin on the receiver input and the transmitter output on the TXD pin.
Figure 31-28. Normal Mode Configuration
31.6.7.2 Automatic Echo Mode
Automatic echo mode allows bit-by-bit retransmission. When a bit is received on the RXD pin, it is sent to the TXD
pin, as shown in Figure 31-29. Programming the transmitter has no effect on the TXD pin. The RXD pin is still
connected to the receiver input, thus the receiver remains active.
Figure 31-29. Automatic Echo Mode Configuration
D0 D1 D2 D3 D4 D5 D6 D7
TXD
Start
Bit
Parity
Bit
Stop
Bit
Baud Rate
Clock
TG = 4
Write
US_THR
TXRDY
TXEMPTY
RTS
Receiver
Transmitter
RXD
TXD
Receiver
Transmitter
RXD
TXD