hdlc external clocks

We are trying ti use the serial ports E & F on RCM5700 module for HDLC frames.

We can configure the serial ports for internal or external clocks (SECR & SFCR registers bits 3:2).

When we use external clock option, are the transmit and receive clocks (TCLKE & RCLKE) inputs or could it be one of them input and the other output? For example if we select internal clocks we know both are outputs.

Jose Luis