Get and Set the Direction Controls

#Firmware/v310

rst_last, dtr_last = cpo:dir( [rts], [dtr] )

This will query and/or set the direction controls for the COM Port.
When transmitting, the handshake lines can be set to flip state to indicate whether receiving or transmitting.

This is crucial for RS485 and SDI-12 interfaces.

e.g.
cpo:dir(0, 2) - sets RS485 standard mode, using DTR to control the direction.