With Mk3 and Mk3/4 controller you can use external jogging keyboard:
Jogging keyboard is connected to controllers JOG header via 16pin ribbon cable.
MK3 JOG header:
Mk3/4 JOG header:
Jogging keyboard connection with Mk3 controller:
Jogging keyboard connection with Mk3/4 controller:
Please read tutorial on how to configure jogging keyboard in PlanetCNC TNG software: