47.7.3.15 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 the following figure.
Setting the USART to operate with hardware handshaking is performed by writing the FLEX_US_MR.USART_MODE field 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 DMAC channel for reception. The transmitter can handle hardware handshaking in any case.
The following figure shows how the transmitter operates if hardware handshaking is enabled. The CTS pin disables the transmitter. If a character is being processed, 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.
If USART FIFOs are enabled (bit FLEX_US_CR.FIFOEN), the RTS pin can be controlled by the USART Receive FIFO thresholds. The RTS pin control through Receive FIFO thresholds can be activated with the FLEX_US_FMR.FRTSC bit. Once activated, the RTS pin will be controlled by Receive FIFO thresholds, set to level 1 each time RXFTHRES is reached and set to level ‘0’ each time RXFTHRES2 is reached (and RXFTHRES is not reached).
