To plug a cardreader into the serial port on a dreambox you have to stop other programs from using the serial port.
In the menus you should select [v] Don't open serial port.
Also check /var/etc/bullz_text.cfg for output to the serial port, and
disable that.
Code:
# 1: Output to the serial port (9600 bps)
# 2: Output to the 'stderr' in your window. This can only be used
# as forground execution. (If background fallback to mode1)
# 3: Output to Unix socket (File name: /tmp/.bullz_console)
# 4: Output to TCP socket (Port Number: 4252 [ BT as hex ]);
#
console: 3
brg.