How do I use the CTCSS sub-channel function on the RT628?

Press the Menu button twice so the current CTCSS sub-channel number and DCS code blink on the LCD. Press the Up (▲) or Down (▼) buttons to select one of the 38 sub-channels (1-38) and the desired DCS code (39-121), then press PTT to confirm. You can turn off the sub-channel function by setting it to 0 (Null).