Siemens SIMATIC S7 System Manual page 256

Program instructions
7.6 Counters
Example CTUD count up/down
LAD
Timing diagram
256
I0.0 counts up
I0.1 counts down
I0.2 resets current value to 0
Count Up/Down counter C48 turns on
C48 bit when current value >= 4
STL
Network 1
LD I0.0
LD I0.1
LD I0.2
CTUD C48, +4
Network 2
LD C48
= Q0.0
System Manual, V2.3, 07/2017, A5E03822230-AF
S7-200 SMART