The frontpanel (both buttons and LEDs) are connected to the UART (AUART0 if i remember correctly); it runs at 1MBit/s.
To set the LEDs, you have to send one byte; the upper nibble indicates which LEDs to update, the lower nibble is a bitmask. So, "33" for example would enable SINGLE and REF, but disable MATH and the red RUN/STOP led, and leave the other LEDs alone.
1x 1 rot. button
2 CH1
4 CH2
8 CH3
2x 1 CH4
2 LA
4 SOURCE
8 RUN/STOP green
3x 1 SINGLE
2 REF
4 MATH
8 RUN/STOP red
4x 1 trigger single
2 trigger normal
4 trigger auto
The button presses are little bit complicated, any pressed button generates a packet starting with "AA", then 9 bytes, and then something that appears to be a checksum. I guess with just a little bit of observation it can be figured out.