I have no experience with SPD-20, but afaik, none of the trigger inputs from the internal pads, external trigger inputs and hihat control send any MIDI output all by themselves. Instead, their trigger signals go into the trigger interface section, where they are converted into different (MIDI) messages which then go either into the internal sound engine or outside world (MIDI OUT).
The SPD-20 user manual should have something about setting up the external trigger inputs to send to MIDI OUT, if that is not set up by default?
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