Rockwell Automation 1757-SWKIT5000 ProcessLogix R500.1 Installation and Upgrade Guide - Manual (Page 266)

Publication 1757-IN500A-EN-P - September 2002
11-26 Performance and Capacity Specifications
I/O Module Publication Periods
Special Considerations The following paragraphs describe known problems and limitations found in
this release.
Device Control May Generate Nuisance Alarms
Error Indication: DevCtl generates a Command Disagree alarm that returns
to normal at the same time.
Description: Problem occurs when a DevCtl block is commanded to
different states very quickly, i.e. as soon as the DevCtl PV feedback reaches the
first OP state commanded, then a different OP command is provided. When
this different state command after a previous command happens along with a)
the internal DevCtl Command Disagree timer expiring, and b) PV changing to
the previous commanded state during the same execution cycle of the DevCtl,
then the nuisance alarm will be generated.
Recovery: Nuisance Command Disagree alarm can safely be ignored.
Workaround: None.
Table 11.W I/O Module Publication Period Specifications
Input Module types Publication Period
Typical Input Module
Includes 1757/1756, 1797-FLEX Ex and 1794-FLEX I/O input
modules, and CN2FFs with exceptions noted below 25 ms
High Density / Non-Isolated Analog Input Module (1756-IF16) 250 ms
RTD Module (1756-IR6I) 50 ms
Thermocouple Module (1756-IT6I) 50 ms
Serial Interface Module (TC-MUX021) 250 ms
Digital Input Module used by 5 ms CEE (local only) 1 ms
For CMs which contain associated input channels, it is recommended that the CM
execution period should be set to at least double the input module sampling period.
Output Module Type Publication Period
Typical Output Module
1757/1756,1797-FLEX EX, and 1794-FLEX I/O Output Modules 50 ms
Input/Output Module Type Publication Period
PFB Module (SST-PFB-CLX)
Note: Update rate is configurable on the PBIM block. Default = 25 ms
Minimum =
12.5 ms (remote chassis)
5 ms (local chassis)
Maximum = 50 ms