fbe0 is read only it seems
bits 7..4 seem to be related to the dip switches on the CSD
bit 7 seems to be fixed to GND/0v.
bit 6,5 is the timer value. It is the time allowed between choosing next cartridge to play.
bit 6, bit 5
off off = 8 1 1
on off = 24 0 1
on on = 32 0 0
bit 4 seems to be timer on/off for time limited play. fbe0 bits 3..0 are defined by the dial bit 3 is ignored.
0 = forever?
1 = 8s,
2 = 56s
fbe2 is read only it seems bits 7..3 are the currently selected cartridge bits 3..0 ??? fbe1 is writeable bits 7,6: ??? bits 5..0: are cartridge number?? fbe3 is writeable: bits 7..4: are cartridge number bits 3..0: ???
== The CSD System Cartridge ==