Rockwell Automation 1771-QRD PULS FLOWMTR - Manual (Page 11)

Introduction
Chapter 2
2–3
The following is a step-by-step example of the information flow to and
from a 1771–QRD Module (Figure 2.2):
1. External devices (magnetic pickups, single channel encoders)
generate signals that are conducted to the 1771–QRD module.
2. The 1771–QRD module converts the incoming signals into counts
and rates, then stores these values until the PLC requests a transfer of
data.
3. When instructed by the ladder program, the processor performs a
Block Transfer Read of the values and stores them in the processor’s
data table.
4. In the case of a count overflow, the ladder program can sense the
overflow and reset the overflow flag, if desired, using data from
within a Block Transfer Write command. Any or all of the totalizers
can also be reset. (Note that when the totalizers are reset the overflow
flags are also reset.)
5. In the case of a rate overrange, the ladder program can sense the
overrange condition and act upon it accordingly.
6. The ladder program can use and/or move the data before it is written
over by the transfer of new data in a subsequent block transfer.
Figure 2.2
Information flow through a programmable controller/1771-QRD System
In this chapter you read about the functional aspects of the 1771–QRD
Module and how it communicates with a Programmable Controller.
How the 1771-QRD
Communicates With
Programmable Controllers
Chapter Summary