Siemens SIMATIC S7-200 System Manual page 136

S7-200 Programmable Controller System Manual
When you use counting modes 6, 7, or 8, and rising edges on both the up clock and down clock
inputs occur within 0.3 microseconds of each other, the high-speed counter could see these
events as happening simultaneously. If this happens, the current value is unchanged and no
change in counting direction is indicated. As long as the separation between rising edges of the
up and down clock inputs is greater than this time period, the high-speed counter captures each
event separately. In either case, no error is generated and the counter maintains the correct count
value.
Count
Up
Clock
Count
Down
Clock
Counter
Current
Value
Figure 6-24 Operation Example of Modes 6, 7, or 8
Phase A
1
Clock
0
Phase B 1
Clock
0
Counter
Current
Value
0
Figure 6-25 Operation Example of Modes 9, 10, or 11 (Quadrature 1x Mode)
122
Current value loaded to 0, preset loaded to 4, initial counting direction set to up.
Counter enable bit set to enabled.
1
0
1
0
2
1
0
Current value loaded to 0, preset loaded to 3, initial counting direction set to up.
Counter enable bit set to enabled.
PV=CV interrupt
generated
3
2
1
PV=CV interrupt generated
PV=CV interrupt generated and
Direction Changed interrupt generated
5
4
4
3
PV=CV interrupt generated and
Direction Changed interrupt generated
4
3
3
2
1
2