Rockwell Automation 1794-VHSC 1794 FLEX I/O Very High Speed Counter Module User Manual - Manual (Page 14)

6 Rockwell Automation Publication 1794-UM010D-EN-E - July 2013
Overview of the Very High Speed Counter Module
Preset Value
Each of the 2 counters has one preset value associated with it. In the encoder or
counter modes, the preset value represents a reference point (or count) from
which the module begins counting. The module can count either up or down
from the preset value. Preset values are loaded into the count registers through the
preset count bits. Preset values can range from 0 to 16,777,215 binary.
Rollover Value
Each of the 2 counters has one rollover value associated with it. When the
rollover value is reached by the encoder/counter, it resets to 0 and begins
counting again. The rollover values range from 1 to 16,777,216 binary. The
rollover value is circular. For example: if you program 360, the count will be from
358, 359, 0, 1, and so on, in a positive direction and from 1, 0, 359, 358, and so
on, in a negative direction.
Software Reset
The counters can also be reset by the Reset Count bits found in Word 0, bits 0
and 4 of the Counter Control word. When one of these bits is set to 1, the
associated counter is reset to zero and begins counting. The module can also be
reset with the gate/reset as explained below. For more details, .
Gate/Reset Input
There is one gate/reset input for each of the 2 counters. The gate/reset input,
when active, will function in one of the 4 store count modes outlined below.
Scaling Input Count at the Gate/Reset Terminal
You can scale the incoming count at the gate/reset terminal. Scaling allows the
incoming pulses at gate/reset to be divided by a number in the range of 1, 2, 4, 8,
16, 32, 64 and 128.
Store Count
The store count feature allows the module to store the current count value of the
associated counter. The store count feature is triggered by the state of the gate/
reset terminal on the module. The stored count of each counter is placed in a
separate word in the Read Data file. The stored count value will remain in the
Read Data file until a new trigger pulse is received at the Gate/Reset terminal.
When a new trigger pulse is received, the old count value will be overwritten by
the new value.
In mode 1, store/continue (see Figure Store/Continue on page 7 ), the leading
edge of a pulse input on input Z (gate/reset) terminal causes the current value in