AT91RM3400-DK Atmel, AT91RM3400-DK Datasheet - Page 284

• Manufacturer Part Number: AT91RM3400-DK
• Description: KIT DEV FOR AT91RM3400
• Manufacturer: Atmel
• Series: AT91SAM Smart ARMr
• Type: MCUr

Specifications of AT91RM3400-DK

• Contents: Evaluation Board, Software and Documentation
• Processor To Be Evaluated: AT91RM3400
• Data Bus Width: 32 bit
• Interface Type: RS-232, USB
• For Use With/related Products: AT91RM3400
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Receive Break
Hardware
Handshaking
Figure 106. Receiver Behavior when Operating with Hardware Handshaking
284
RXBUFF
US_CR
Write
RXD
RTS
AT91RM3400
RXEN = 1
The receiver detects a break condition when all data, parity and stop bits are low. This corre-
sponds to detecting a framing error with data at 0x00, but FRAME remains low.
When the low stop bit is detected, the receiver asserts the RXBRK bit in US_CSR. This bit
may be cleared by writing the Control Register (US_CR) with the bit RSTSTA at 1.
An end of receive break is detected by a high level for at least 2/16 of a bit period in asynchro-
nous operating mode or one sample at high level in synchronous operating mode. The end of
break detection also asserts the RXBRK bit.
The USART features a hardware handshaking out-of-band flow control. The RTS and CTS
pins are used to connect with the remote device, as shown in Figure 105.
Figure 105. 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 transmit-
ter can handle hardware handshaking in any case.
Figure 106 shows how the receiver operates if hardware handshaking is enabled. The RTS
pin is driven high if the receiver is disabled and if the status RXBUFF (Receive Buffer Full)
coming 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 107 shows how the transmitter operates if hardware handshaking is enabled. The CTS
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.
USART
RXD
TXD
CTS
RTS
RXD
TXD
RTS
CTS
Remote
Device
RXDIS = 1
1790A–ATARM–11/03