Siemens SIMATIC S5-100U System Manual page 186

STEP 5 Operations
Setting a Counter "S" and Counting Down "CD"
Example:
When input I 0.1 is switched on (set), counter 1 is set to count 7. Output Q 1.0 is now "1".
Every time input I 0.0 is switched on (count down), the count is decremented by 1.
The output is set to "0" when the count is "0".
Timing Diagram
1
0
1
0
7
0
1
0
S C 1
STL
A I 0.0
CD C 1
NOP 0
A I 0.1
L KC 7
S C 1
NOP 0
NOP 0
NOP 0
A C 1
= Q 1.0
8-28
I 0.0
I 0.1
C 1
Q 1.0
Time
S C 1
CSF
C 1
I 0.0
CD
CU
I 0.1
S
KC 7
CV BI
DE
Q 1.0
R Q
Circuit Diagram
I 0.1
KC 7
R S CI
I 0.0
I I I I
CQ
0
Count
Q 1.0
LAD
C 1
I 0.0
CD
CU
I 0.1
S
KC 7
CV BI
DE
R Q
EWA 4NEB 812 6120-02b
S5-100U
Binary
16 bits
Q 1.0