SAM7S256_14 Datasheet, PDF (378/775 Pages) ATMEL Corporation – ARM-based Flash MCU

Figure 31-18. Break Transmission
Baud Rate
Clock
TXD
Write
US_CR
Start
Bit
D0
D1
D2
D3
D4
D5
D6
D7
Parity Stop
Bit Bit
STTBRK = 1
TXRDY
TXEMPTY
Break Transmission
STPBRK = 1
End of Break
31.6.3.11 Receive Break
The receiver detects a break condition when all data, parity and stop bits are low. This corresponds 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 writ-
ing 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 asynchronous operating mode
or one sample at high level in synchronous operating mode. The end of break detection also asserts the RXBRK
bit.
31.6.3.12 Hardware Handshaking
The USART features a hardware handshaking out-of-band flow control. The RTS and CTS pins are used to con-
nect with the remote device, as shown in Figure 31-19.
Figure 31-19. Connection with a Remote Device for Hardware Handshaking
USART
TXD
RXD
CTS
RTS
Remote
Device
RXD
TXD
RTS
CTS
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 synchro-
nous 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 31-20 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. Nor-
mally, the remote device does not start transmitting while its CTS pin (driven by RTS) is high. As soon as the
SAM7S Series [DATASHEET]
6175M–ATARM–26-Oct-12
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