Rockwell Automation 1771-IFE ANALOG INPUT MODULE - Manual (Page 31)

3–5 Module Programming
Publication 1771Ć6.5.115 - February 1999
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
calibration check “3” (if requested), 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. (If RTS is enabled, a BTR will only occur after the specified
time period. Refer to chapter 4.)
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.
Module Scan Time