Rockwell Automation 1771-IR Series D RTD Input Module User Manual - Manual (Page 28)

3–6 Module Programming
Publication 1771Ć6.5.129 - March 2000
A subsequent BTW operation is enabled by a pushbutton switch
(rung 2). Changing processor mode will not initiate a block transfer
write unless the first pass bit is added to the BTW input conditions.
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 specifications,
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 and loaded
calibration constants “2”, scanned the inputs “3”, and filled the data
buffer “4”. Write block transfers, therefore, should only be
performed when the module is being configured or calibrated.
Any time after the second scan begins “5”, a BTR request “6” can
be acknowledged.
When operated in real time sample mode (RTS) = 00, a BTR may
occur at any time after “4.” When operated in RTS = T, a BTR will
be waived until ”T” milliseconds, at which time 1 BTR will be
released.
Figure 3.4
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 7 8 9
Internal Scan time = 50msec
T = 100ms, 200ms, 300ms ... 3.1sec.
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