Ja weil printf() als erstes Argument einen FormatString erwartet. Habs oben angepasst.

sast

PS: Falls du mit der Keil Software C51 arbeitest, gibts auch schon die _getkey() Funktion, die genau das selbe macht wie mein b_getkey().

Code:
_getkey
Summary: #include <stdio.h>
char _getkey (void);
Description: The _getkey function waits for a character to be received
from the serial port.
NOTE
This routine is implementation-specific, and its function may
deviate from that described above. Source is included for
the _getkey and putchar functions which may be modified to
provide character level I/O for any hardware device. Refer
to “Customization Files” on page 150 for more information.
Return Value: The _getkey routine returns the received character.