This video from Hispabrick magazine demonstrates it perfectly:
PRESS and RELEASE the green buttons on both devices and WAIT until they connect, the lights on the devices will match.
Lots of people have problems with this step, either they keep the buttons pressed (which will cause the devices to switch themselves off) or they don't have the patience to wait the couple of seconds until the devices connect and repress one of the buttons in which case the connection cycle restarts...
When connected there seem to be 3 modes:
- mode 1 controls A and B, i.e. the internal motors
- mode 2 controls B and A, i.e. the internal motors in reversed order
- mode 3 controls the external ports C and D, you can connect various motors, but also a train motor and external leds. The latter two don't operate in bang-bang mode (all on or all off) but you can set the speed/intensity gradually...
- There seems to be no mode where D and C or switched, or that an internal motor and external port are combined (e.g. "A and C" or "B and D")
You apparently cycle between the modes by shortly pressing (and releasing) the green button on both devices, the lights on the devices change (and match) when successful.
Regarding firmware updates, keep your app up to date on your Android device and it will automatically upload any firmware updates as soon as you connect a Powered Up device. You'll notice by the cycling colors the device displays while updating, it may take a few minutes,... It's a bad idea to interrupt any firmware update so please be patient.