Datasheet

 2017 Microchip Technology Inc. DS60001516A-page 465
SAM9G20
31.6.3.15 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 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 asynchronous operating mode or one sample at high
level in synchronous operating mode. The end of break detection also asserts the RXBRK bit.
31.6.3.16 Hardware Handshaking
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 31-27.
Figure 31-27: 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 31-28 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 trans-
mitting 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 31-28: Receiver Behavior when Operating with Hardware Handshaking
Figure 31-29 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.
Figure 31-29: Transmitter Behavior when Operating with Hardware Handshaking
USART
TXD
CTS
Remote
Device
RXD
TXDRXD
RTS
RTS
CTS
RTS
RXBUFF
Write
US_CR
RXEN = 1
RXD
RXDIS = 1
CTS
TXD