Dec_6_Counters ($F55E)
These routines check all six of the default counters at $C82E-$C833 and decrements those which are not already zero.
EXIT:
X-reg points to the default counters at $C82E B-reg = $FF All other registers preserved.
X-reg points to the default counters at $C82E
B-reg = $FF
All other registers preserved.
Source