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Renesas Electronics America - Knowledgebase

Single Pin for CTS/RTS Signals with RX Family

Last Updated:08/25/2017


In the RX family, it seems that input and output of CTS# and RTS# signals are performed on one pin. Should the CTS# and RTS# signals of an RS232C driver be connected directly to this pin?


The CTS enable bit (SPMR.CTSE) determines whether the CTS#/RTS# pin is used exclusively for CTS or RTS functions. Therefore, even if CTS# and RTS# signals from the driver are connected to one pin on the RX, only one of the functions (CTS# or RTS#) can be used.

When you need to control both CTS# and RTS#, connect either of the signals to the CTS#/RTS# pin and connect the other signal to a GPIO port with an external interrupt to perform the CTS or RTS function. 

When using a GPIO port for the RTS function, beginning when reception is disabled, flow control will be late due to port control delay and the other side may start sending. Due to this, please consider using the CTS function for interrupt process. When using a GPIO pin for the CTS function, the transmission timing may be slower because of the time required for software control. Please select which function to use or substitute based on the needs for your own application.
Suitable Products
RX Family