What are the functions of the flow control pins in the USB to UART Bridge Controller (Gen I and Gen II)?
The CTS, RTS, DTR, and DSR pins in the USB to UART Bridge Controller have two functionalities: hardware flow control and I/O. You can use the USBUART configuration utility (for CY7C65225) or USB Serial configuration utility (CY7C65213/CY7C65211/CY7C65215) to reconfigure the controller with either of these functions.
Flow Control. Choose this function if the two UART links have different processing speeds. If the UART receiver has a processing delay between two consecutive receptions over the UART, it can signal ‘wait’ to the UART transmitter by de-asserting the CTS line. When you are ready to send data, the transmitter can use the RTS pin to signal the receiver to keep its receiving line active. The DTR/DSR pin can enable and disable the Transmit/Receive function. The RTS/CTS pin can enable and disable the transfer of individual blocks of data.
I/O. You can choose this function if the UART transmitter and receiver have similar processing speeds. You can use the CTS, RTS, DTR, and DSR pins as general purpose I/Os that can be read and written to from the PC by USB requests. In this mode, CTS and DSR serve as input pins and RTS and DTR serve as output pins.