I trust that I might save the time of others who want to connect UART4 to the Pi-2 UART: It is required to connect the ground of both boards.
I trust that I might save the time of others who want to connect UART4 to
the Pi-2 UART: It is required to connect the ground of both boards.
Generally, two electronic systems talking to each other over wires
(not fiber optics, and not ethernet, which uses isolation techniques)
will need a common ground.
This is especially true of either parallel port driven projects, or
serial (I2C, SPI, CAN, RS-232, to name a few styles).
MIDI uses isolation techniques.
Just as when you measure a voltage, you need to measure with reference
to something (typically a ground point), the other circuits that
respond to that voltage need the same (and common) reference point.
This is true unless there have been fairly special techniques used to
bypass that need.
Remembering this can save you lots of difficulty, however, when in
doubt about connections, ask.
Harvey
Thank you for your reply and explanation.