Rockwell Automation 1771-N SERIES High Resolution Analog Module User Manual - Manual (Page 36)

3–4 Communicating With Your Analog Module
Publication 1771ĆUM127B-EN-P - December 2002
Scan time is defined as the amount of time it takes for the module to
read the input channels and place new data into the data buffer
and/or read the data buffer and write new data to the output channels.
Scan time for your module is shown in Figure 3.3.
Figure 3.3
Block Transfer Time
Block
Transfer
Write
Time
End of Block
Transfer Write
Configure
Time
1st Scan 2nd Scan 3rd Scan
Module available
to perform block transfer
1 2 3 4 5 6
10529ĆI
Internal scan time = 25ms
The following description references the sequence numbers in
Figure 3.3.
Following a block transfer write (1) the module inhibits
communication until after it has configured the data and loaded
calibration constants (2), scanned the inputs and/or outputs (3), and
filled the data buffer (4). Configuration block transfers, therefore,
should only be performed when the module is being configured or
calibrated.
Any time after the buffer is filled (4), a block transfer read (BTR)
request can be acknowledged.
When operated in the default mode, new data will be available for a
BTR every 25 milliseconds. When operated in real time sample
mode
(RTS = T), BTRs will be ignored by the module for “T”
milliseconds, at which time a single BTR will be allowed.
The following are sample programs for using your modules more
efficiently when operating with the PLC-3 or PLC-5 family
processors.
These programs show you how to configure the module and read
data from the module, and efficiently update the output channels on
those modules with outputs.
Refer to the proper PLC-3 or PLC-5 documentation for additional
information on processor programming and data entry.
Module Scan Time
Programming Samples