when used as the master device to control external gear connected by MIDI there are basically 2 different ways of using it:
1) not programmable automatic simple program changing
whenever you select/navigate to a new patch in a given bank, the POD sends always and automatically the corresponding MIDI program change number to any connected slave device set on the same MIDI channel (1-16)..
the POD reference table of MIDI program changes is fixed, and it starts with PC 000 which corresponds to bank1/presetA, then PC 001 corresponds to bank1/presetB, PC 004 corresponds to bank2/presetA, and so on up to the last one PC 063 which corresponds to bank16/presetD..
therefore since the POD table of automatic program changes sent by MIDI is not programmable, you have to program the connected slave device accordingly in order to get the wanted program change when you select a given patch of the POD.
2) flexible and programmable MIDI controlling from within a specific patch
to avoid the automatic fixed program changes, you must stick to a specific POD patch of your choice, specifically programmed to use the POD switches and expression pedals to control the MIDI slave device, in addition to switch on/off and control the POD models (if any) in that patch chain.
each of the POD switches and expression pedals can be programmed to send program changes and or different MIDI controls by MIDI..
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when the POD is used instead as the slave device, thus controlled through MIDI by an external device, what can be controlled are: the selection of the setlist/bank/preset, the looper functions, tap tempo, tuner on/off, and what in any current patch has been assigned to the switches and expression pedals