Technology instructions
10.1 Counting (High-speed counters)
S7-1200 Programmable controller
580 System Manual, V4.2, 09/2016, A5E02486680-AK
Under the Event configuration section, you can select a hardware interrupt OB from the
dropdown menu (or you can create a new OB) and attach it to an HSC event. The priority of
the interrupt is in a range from 2 to 26, where 2 is the lowest priority and 26 is the highest
priority. Depending on the HSC’s configuration, the following events are available:
● Counter value equals reference value event: A counter value equals reference value
event occurs when the HSC’s count value reaches the reference value. You can set the
reference value during configuration under the Initial reference value section, or by
updating "NewReference1" using the CTRL_HSC_EXT instruction. Refer to the
"Operating phase (Page 574)" section for further information.
● Synchronization event: A Sync (synchronization) occurs whenever you enable and trigger
the Sync input.
● Change of direction event: A change of direction event occurs when the counting
direction changes. Refer to the "Operating phase (Page 574)" section for further
information.
Hardware input pin assignment
For each HSC input that you enable, select the desired input point, located either on the
CPU or optional signal board (communication and signal modules do not support HSC
inputs). When you select a point, STEP 7 displays the maximum frequency value next to the
selection. The digital input filter settings may need to be adjusted so that all valid signal
frequencies can pass through the filter. To set up the HSC input filters, refer to "Configuring
digital input filter times (Page 172)".
Note
CPU and SB input channels (V4 or later firmware) have configurable input filter times
Earlier firmware versions had fixed HSC input channels and fixed filter times that you could
not change.
With V4 or later versions, you can assign input channels and filter times. The default input
filter setting is 6
.4 ms, which limits the maximum counting rate to 78 Hz. You can change the
filter settings to count higher or lower frequencies depending on the design of your system.
Risks with changes to filter time setting for digital input channels
If the filter time for a digital input channel is changed from a previous setting, a new "0"
level input value might need to be presented for up to a 20.0 ms accumulated duration
before the filter becomes fully responsive to new inputs. During this time, short "0" pulse
events of duration less than 20.0 ms may not be detected or counted.
The changing of filter times can result in unexpected machine or process operation, which
can cause death or serious injury to personnel, and/or damage to equipment.
To ensure that a new filter time goes immediately into effect, power cycle the CPU.
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