Optional dynamic hardware flow control

When the interface MCU receives a Data Terminal Ready (DTR) signal from a terminal, it performs automatic Hardware Flow Control (HWFC) detection.

HWFC detection

Automatic HWFC detection is done by driving Clear to Send (CTS) from the interface MCU and evaluating the state of Request to Send (RTS) when the first data is sent or received. If the state of RTS is high, it is assumed HWFC is not in use. If HWFC is not detected, pins P0.10/P0.21 (CTS) and P0.11/P0.19 (RTS) are free for the nRF application to use.

After a power-on reset of the interface MCU, all UART lines are tri-stated when no terminal is connected to the virtual serial port. If HWFC has been used and detected, P0.10/P0.21 (CTS) is driven by the interface MCU until a power-on reset has been performed or until a new DTR signal is received and the detection is redone.

Note: When using trace functionality, HFWC on UART_0 must be disabled. For more information, see Debug input and trace.

Using HWFC pins for other tasks

To disconnect the pins used by a UART for HWFC, perform the following tasks.

Switch SW7 for the selected UART to the OFF position. This disconnects the line from the interface MCU.
Cut the solder bridges for P1.01/P0.20 (TXD) and P1.00/P0.22 (RXD). This ensures they are not affected by the interface MCU. The lines can be resoldered later if needed.