according to the RC500 manual (p21) the RC500 reacts on MIDI Clock and MIDI Start/Stop when you set the RC-500's MIDI SYNC to 'AUTO'

On Fri, Jan 6, 2023 at 06:18 PM, FourPaws wrote:

SysEx F0 41 10

Actually this isn't even part of the SysEX realtime standard. It looks like a Roland propriety Sysex message.

There is a difference between MIDI SysEX realtime start and stop commands (as you show above) and standard MIDI  start and stop commands.  Normal Transport Start and Stop Commands are simply FA and FC respectively. Maybe that is what the RC500 is looking for.

On top of that you might need to send MIDIClock messages with a certain BPM for the MIDIStart message to do anything. ("SendRealtime MIDIClock 100 BPM")
I believe the official MIDI spec says that playback or recording of a sequencer for instance starts on the first MIDIClock message following the MIDIStart. If the receiving device follows that spec, it will not react on the MIDIStart message if there is no MIDIClock. Some devices might not follow that spec and react immediately on the MIDIStart message, so this is just for your info - in case you wonder why nothing happens while you do send MIDIStart/MIDIStop messages. 

If you're just using the UnO (not 2) firmware, I don't believe you can.  Start is a MIDI System Message, and no equivalent CC message exists.  If you're using UnO2, the command is:

SendRealtime MIDIStart

Hi all...

Simple question... How do I send the "MIDI Start (FA)" command...???

Thanks..!!!