Rockwell Automation 1771-VHSC , D17716.5.74 Very High S - Manual (Page 25)

1–17 Overview of the Very High Speed Counter Module
The default mode for the VHSC module is the counter mode for all 4
of the counters. In the default configuration, the module will
continuously return counts (0-999,999 binary) to the programmable
controller processor. The presets and rollovers associated with each
of the 4 counters will not be active, nor will any of the outputs be
active.
The processor transfers data to and from the module using block
transfer write (BTW) and block transfer read (BTR) instructions in
your ladder diagram program. These instructions let the processor
obtain input values and status from the module, and let you establish
the module’s mode of operation (1.13).
Figure 1.13
How the Module Communicates with a Programmable
Controller
User Program
PC Processor
(PLCĆ5/15 Shown)
VHSC Module
1771ĆVHSC
BTW
BTR
5
6
2
3
12933ĆI
4
1
Data Table
1. The processor transfers your configuration data and commands to
the module using a BTW instruction.
2. External devices generate input signals that are transmitted to the
module.
3. The module converts these signals into binary or BCD format,
and stores these values and controls their output until the
processor requests their transfer.
4. When instructed by your ladder program, the processor performs
a BTR of the values and stores them in a data table.
5. The processor and module determine that the transfer was made
without error, and that input values are within a specified range.
How the Module
Communicates with a
Programmable Controller