A little on channel steering
It is possible to remotely change the channel on a MOTOTRBO mobile by applying a high or low to the accessory connector pins that are configured as Channel Select.
BCD number of the channel.
Debounce prevents a bad electrical contact from producing a false trigger. The debounce time can also be set and the default of 100ms works for 99% of applications. If you are triggering these inputs with a transistor or IC, you dont really need to be concerned about debounce.
Logic low is 0-2Vdc and logic high is 5-12Vdc. The input goes into a transistor so if you're going to be connecting this to external equipment some distance away or powered from a different supply line then you should seriously consider electrical isolation (optocoupler). If you want to switch channels by means of a remote up down switch, you can use a microcontroller or a counter IC like this one.
Here are the pin locations: