Rockwell Automation 1771-QRD PULS FLOWMTR - Manual (Page 33)

Chapter 5
5–1
More on Overrange and Overflow
In this chapter you will learn more about the overrange and overflow status
flags sent from the QRD to the PLC. You will also learn how to use a
Block Transfer Write to clear the overflow bits, the totalizers or any
combination of both.
As discussed in Chapter 4, an overflow occurs when the value of any of the
four totalizers exceeds the maximum value of 32,767. At that time, an
overflow flag for that channel is set and can be seen in the first word of the
Block Transfer data table. These overflow flags can be reset by the ladder
logic. Any or all of the totalizers can also be reset either independently of
each other, or they can all be reset simultaneously.
When it detects an overflow, the 1771–Q RD sets an overflow flag in the
acknowledge word (word 000) of the Block Transfer Read response. The
best way to understand this concept is to break down the acknowledge
word into bit format. The 16 bits are grouped by function into four
categories (Figure 5.1):
Figure 5.1
Acknowledge Word (From 1771-QRD Module)
Table 5.A
Error Codes from Acknowledge Word
Code Meaning
0 Valid Data
1 Channel Pair Fault
2 BLOCK TRANSFER Syntax Error
4 Channel Pair Fault and Syntax Error
Chapter Objectives
Frequency Overrange Flags