The Amstrad CSD was a machine that was in-store to demonstrate the hardware of the Amstrad plus.
It had a system cartridge which contained a menu, and could hold a furthur 12 cartridges.
It has additional hardware to allow switching of cartridges.
Technical
The information was derived from the software. It is not completely accurate. Lots of information is not known at this time.
It uses ports fbe0-fbe3. The exact decoding of these ports is unknown.
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 off on = 16 1 0 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: ???