Siemens SIMATIC S7-200 System Manual page 129

Example: SIMATIC Count Down Counter Instruction
Timing Diagram
Example: SIMATIC Count Up/Down Counter Instruction
Timing Diagram
I0.0 (up)
I0.1 (down)
I0.2 (reset)
C48 (current)
C48 (bit) Q0.0
Network 1 //Count down counter C1 current value
//counts from 3 to 0
//with I0.1 off,
//I0.0 Off- -on decrements C1 current value
//I0.1 On loads countdown preset value 3
LD I0.0
LD I0.1
CTD C1, +3
Network 2 //C1 bit is on when counter C1 current value = 0
LD C1
= Q0.0
I0.0 Down
I0.1 Load
3
2
1
0
0
C1 (current)
C1 (bit) Q0.0
Network 1
LD I0.0
LD I0.1
LD I0.2
CTUD C48, +4
Network 2
LD C48
= Q0.0
4
3
2
1
0
S7-200 Instruction Set
3
2
//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
5
5
4
4
3
Chapter 6
0
115