Rockwell Automation 1771-VHSC , D17716.5.74 Very High S - Manual (Page 15)

1–7 Overview of the Very High Speed Counter Module
Rollover Value
Each of the 4 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 0 to
999,999 binary or BCD (0 represents 1,000,000). The rollover value
is circular (for example: if you program 360, the count will be from
358, 359, 0, 1 etc. in a positive direction and from 1, 0, 359, 358 etc.
in a negative direction).
Software Reset
The counters can also be reset by the Reset Count bits found in Word
1, bits 0-3 of the block transfer write. 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.
Refer to chapter 4 for further details.
Gate/Reset Input
There is one gate/reset input for each of the 4 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. Refer to words 21 to 24 in
the BTW file (chapter 4).
Store Count
The store count feature allows the module to store the current count
value of any (or all) of the four counters. 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
Block Transfer Read file (words 11-18 respectively). The stored
count value will remain in the block transfer read 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.
The store count feature is selected by words 3 and 4 of the block
transfer write initialization file. Refer to chapter 4 for further details.