start - operation - errors
What is it
The Roland A-880 can be seen as a digital patch bay. You can digitally connect one physical INPUT Port to 0 to 8 physical OUTPUT Ports (=MIDI Splitter). Already assigned OUTPUT Ports can not be assigned to a second INPUT Port. You can only merge 2 INPUT Ports together, the IN Port to which the remote control to the A-880 is assigned, and the IN Port to which the MIDI Clock signal is assigned. Both functions can also be performed by one IN Port. When you assign these functions to different IN Ports, the "normal" MIDI signals to these Ports will also be merged and relayed to OUT Ports.
Remote control from MIDI consists of 2 different possibilities: you can select a different patch setting from the A-880 memory with a MIDI Program Change message, and you can completely control the A-880 using SysEx messages. Software exists that is able to perform all the front panel operations with a nice graphical interface on your Windows or Apple computer. Search for "A-880 Mountain Utilities".
After a Factory Reset, IN Port 1 is set to receive the Remote Control data and IN Port 2 is set to receive the MIDI Clock data. This way, these 2 Ports are merged and the output signal is split to OUT Port 1 and 2. The IN Port 3 is connected to OUT Port 3, IN 4 to OUT 4, and so on.
I don't understand why Roland implemented the merging of only 2 IN Ports.