at91sam9g20-cu ATMEL Corporation, at91sam9g20-cu Datasheet - Page 483

• Manufacturer Part Number: at91sam9g20-cu
• Description: At91 Arm Thumb Microcontrollers
• Manufacturer: ATMEL Corporation

Figure 32-28. Receiver Behavior when Operating with Hardware Handshaking
6384B–ATARM–15-Dec-08
RXBUFF
US_CR
Write
RXD
RTS
RXEN = 1
Figure 32-27. Connection with a Remote Device for Hardware Handshaking
Setting the USART to operate with hardware handshaking is performed by writing the
USART_MODE field in the Mode Register (US_MR) to the value 0x2.
The USART behavior when hardware handshaking is enabled is the same as the behavior in
standard synchronous or asynchronous mode, except that the receiver drives the RTS pin as
described below and the level on the CTS pin modifies the behavior of the transmitter as
described below. Using this mode requires using the PDC channel for reception. The transmitter
can handle hardware handshaking in any case.
Figure 32-28
pin is driven high if the receiver is disabled and if the status RXBUFF (Receive Buffer Full) com-
ing from the PDC channel is high. Normally, the remote device does not start transmitting while
its CTS pin (driven by RTS) is high. As soon as the Receiver is enabled, the RTS falls, indicating
to the remote device that it can start transmitting. Defining a new buffer to the PDC clears the
status bit RXBUFF and, as a result, asserts the pin RTS low.
Figure 32-29
pin disables the transmitter. If a character is being processing, the transmitter is disabled only
after the completion of the current character and transmission of the next character happens as
soon as the pin CTS falls.
Figure 32-29. Transmitter Behavior when Operating with Hardware Handshaking
shows how the transmitter operates if hardware handshaking is enabled. The CTS
shows how the receiver operates if hardware handshaking is enabled. The RTS
CTS
TXD
USART
TXD
RXD
CTS
RTS
AT91SAM9G20 Preliminary
RXD
TXD
RTS
CTS
Remote
Device
RXDIS = 1
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