Rockwell Automation 1771-IFF/A,D17716.5.116 FAST ANALOG INPUT MODULE - Manual (Page 55)

6-5
Publication 1771Ć6.5.116 - June 1996
The real time sampling (RTS) mode of operation provides data
gathered at precisely timed intervals for use by the processor. BTW
word 3 bits 11–15 (13–17 octal) are used to set the real time
sampling interval.
RTS is invaluable for time based functions (such as PID and
totalization) in the PLC. It allows accurate time based calculations in
local or remote I/O racks. In the RTS mode the module scans and
updates its inputs at a user defined time interval (T) instead of the
default interval. The module ignores block transfer read (BTR)
requests for data until the sample time period elapses. The BTR of a
particular data set occurs only once at the end of the sample
period and subsequent requests for transferred data are ignored
by the module until a new data set is available. If a BTR does not
occur before the the end of the next RTS period, a time-out bit is set
in the BTR status area. When set, this bit indicates that at least one
data set was not transferred to the processor. (The actual number of
data sets missed is unknown.) The time-out bit is reset at the
completion of the BTR.
Set appropriate bits in the BTW data file to enable the RTS mode.
You can select RTS periods ranging from 100 milliseconds (ms) to
3.1 seconds. Refer to the table below for actual bit settings. Note
that the default mode of operation is implemented by placing all
zeroes in bits 11–15 (13–17 octal).
Bit Settingsfor the Real Time Sample Mode
Decimal Bits 15 14 13 12 11
Sample Time Period
15 14 13 12 11
Sample Time Period
Octal Bits 17 16 15 14 13
Sample Time Period
17 16 15 14 13
Sample Time Period
0 0 0 0 0 No RTS, Default settings 1 0 0 0 0 1.6s
0 0 0 0 1 100ms 1 0 0 0 1 1.7s
0 0 0 1 0 200ms 1 0 0 1 0 1.8s
0 0 0 1 1 300ms 1 0 0 1 1 1.9s
0 0 1 0 0 400ms 1 0 1 0 0 2.0s
0 0 1 0 1 500ms 1 0 1 0 1 2.1s
0 0 1 1 0 600ms 1 0 1 1 0 2.2s
0 0 1 1 1 700ms 1 0 1 1 1 2.3s
0 1 0 0 0 800ms 1 1 0 0 0 2.4s
0 1 0 0 1 900ms 1 1 0 0 1 2.5s
0 1 0 1 0 1.0s 1 1 0 1 0 2.6s
0 1 0 1 1 1.1s 1 1 0 1 1 2.7s
0 1 1 0 0 1.2s 1 1 1 0 0 2.8s
0 1 1 0 1 1.3s 1 1 1 0 1 2.9s
0 1 1 1 0 1.4s 1 1 1 1 0 3.0s
0 1 1 1 1 1.5s 1 1 1 1 1 3.1s
Default Settings = SingleĆended inputs Ć 25 ms
Differential inputs Ć 12.5 ms
Real Time Sampling