Rockwell Automation 1771-IXHR , D17716.5.80 HIGH RESOL.THERMOCOUPLE - Manual (Page 23)

Module Programming
Chapter 4
4Ć5
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 4.3.
The following description references the sequence numbers in Figure 4.3.
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 “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
25 milliseconds. When operated in RTS = T, BTR will be waived until
”T”millseconds, at which time 1 BTR will be released.
Figure 4.3
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 7 8 9
10529-I
Internal Scan time = 25msec
T = 25ms, 50ms, 75ms ... 3.1sec.
In this chapter, you learned how to program your programmable controller. You
were given sample programs for your PLC–3 and PLC–5 family processors.
You also read about module scan time.
Module Scan Time
Chapter Summary