Rockwell Automation 1756-LSC8XIB8I ControlLogix Low-speed Counter Module - Manual (Page 75)

Rockwell Automation Publication 1756-UM536A-EN-P - April 2012 75
Tag Definitions Appendix B
IMPORTANT Keep in mind the following when using frequency as a window comparison
method:
• When configured to compare frequency values, window On/Off values are
still DINT (32-bit signed integers) while the returned frequency values are
REAL (32-bit IEEE float). As a result, the frequency triggers for On/Off
windows can only be defined in 1 Hz increments.
• Fluctuations in high frequency values across window parameters could
cause the window to transition on each pulse if the input frequency is at a
window parameter and you are using instantaneous frequency as the
comparison method. In this case, the module will produce a COS message
on the backplane with each input. This high traffic could result in system
communication issues.
• For example, if you set a window Off value at 18 kHz, and the input is at
18 kHz, the instantaneous frequency calculation could result in frequency
fluctuations for each pulse between 17998.0 Hz and 18002.0 Hz. This
fluctuation would cause a COS message to be sent every 55 μs. If this
situation occurs for all eight counters, the module can generate a large
amount of backplane traffic possibly resulting in system communication
issues.
Table 7 - Counter Module Output Tags
Name Data Type Definition
Counter[x].DisableCount BOOL Disable Count—When set, Counter[x] will not count.
0 = Counting occurs unless the Counter[x].CountEnTieToPt configuration tag prevents counting.
1 = Counting is disabled.
Counter[x].ResetCount BOOL Reset Count—Resets the count back to zero on a rising edge. The Counter[x].ResetTieToPt configuration tag can also
trigger a count reset on a rising edge.
0 = Disabled
1 = Enabled
Counter[x].PresetCount BOOL Preset Count—Sets the count to the preset value stored in the Counter[x].Preset output tag on a rising edge. The
Counter[x].PresetTieToPt configuration tag can also transition the count to the preset value on a rising edge.
0 = Disabled
1 = Enabled. The count transitions to the preset value on a rising edge.
Counter[x].CountDown BOOL Count Down—Controls the direction of a count if the Counter[x].UpDownTieToPt input tag is not enabled for the
corresponding counter.
0 = The count direction is up (default).
1 = The count direction is down.
Counter[x].Rollover DINT Rollover—Defines how many counts accumulate before the count rolls over to zero. The count rolls over to zero on the
rollover value.
The default rollover value is a maximum count of 2
31
.
Counter[x].Preset DINT Preset—Defines the starting value for a count. The preset value must be less than the rollover value. If the preset value is
greater than or equal to the rollover value, the default preset value is used.
The default preset value is zero.
Counter[x].Window0On DINT Window 0 On—Defines the count or frequency value that results in an On status for window 0. The status for window 0
is stored in the Counter[x].InWindow0 input tag.
This tag is used in conjunction with the Counter[x].Window0Off tag to create an On/Off window. If the values in the
Counter[x].Window0On and Counter[x].Window0Off tags are the same, the window is disabled.