Rockwell Automation 1771-IFE , D17716.5.90 USER MNL. ANALOG INPUT Module - Manual (Page 29)

Module Programming
Chapter 3
3-5
Scan time is defined as the amount of time it takes for the input module to
read the input channels and place new data into the data buffer. Scan time
for your module is shown in Appendix A.
The following description references the sequence numbers in Figure 3.4.
Following a block transfer write “1” the module inhibits communication
until after it has configured the data “2,” performed self-calibration “3,”
scanned the inputs “4,” and filled the data buffer “5.” Write block transfers,
therefore, should only be performed when the module is being configured
or calibrated.
Any time after the second scan begins “6,” a BTR request “7” can be
acknowledged. This interrupts the scan and the BTR empties the buffer.
Following the BTR, the input module inhibits block transfer
communications with the programmable controller until it has scanned its
inputs “8” and new data is ready ”9.” The input module repeats the scan
sequence “10,” updating the input values until another block transfer
request is received. Therefore, BTRs will only be completed as frequently
as the total scan time of the input module.
Figure 3.4
Block Transfer Time
1 2 3 4 5 6 7 8 9 10
End of block
transfer write
1st
Scan
Module available to
perform block transfer
Note: Configure/Calibration time:
SingleĆended mode = 100ms without filter, 102ms with filter
Differential mode = 56ms without filter, 58ms with filter
Scan time:
= 12.5 ms for 8 differential inputs (no scaling or digital filter);
= 25 ms for 16 singleĆended inputs (no scaling or digital filter) 12689
2nd
Scan
3rd
Scan
Block
Transfer
Write
time
Configure
time
Calibration
time
See note
In this chapter, you learned how to program your programmable controller.
You were given sample programs for your PLC-2, PLC-3 and PLC-5
family processors.
You also read about module scan time.
Module Scan Time
Chapter Summary