Rockwell Automation 1771-IXE/D Thermocouple/Millivolt Input Module User Manual - Manual (Page 28)

3–6 Module Programming
Publication 1771Ć6.5.130 Ć May 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 Figure 3.4.
The following description references the sequence numbers in Figure
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 block transfer read
(BTR) request “6” can be acknowledged.
When operated in the default mode (RTS) = 00, a BTR will be
released every 50 milliseconds. When operated in RTS = T, BTR will
be waived until ”T”millseconds, 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
10529-I
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