Allen-Bradley ControlLogix 5570 - TOD Instruction Flags and Math Status Flags; Add-On Instructions Do Not Propagate Math Status Flags

130 Rockwell Automation Publication 1756-RM100F-EN-P - October 2018
Chapter 6 Instruction Execution
TOD Instruction Flags and Math Status Flags
This implementation sets math status flags in a consistent manner across
instructions, and offers more complete math status flags for the TOD
instruction.
Mitigation
N/A
Add-On Instructions Do Not Propagate Math Status Flags
When the content of an Add-On Instruction generates a math status flag, the
status is not propagated to the routine or other Add-On Instructions that call
the offending Add-On Instruction. Add-On Instructions are not considered
producers of Math Status Flags. Math status flags can be evaluated in the
Add-On Instruction, but not by the caller.
Mitigation
If you want the Add-On Instruction to return math status flags, then use
Boolean output parameters.
Language Affected
Ladder Logic (RLL) Yes
Structured Text (ST) No
Function Blocks (FBD) No
Sequential Function Chart (SFC) No
5580/5380 Controllers 5570/5370 Controllers
In these controllers, a TOD instruction can modify the
math status flags S:V, S:N, and S:Z.
In these controllers, the TOD instruction only populates
the math overflow condition S:V.
Language Affected
Ladder Logic (RLL) Yes
Structured Text (ST) No
Function Blocks (FBD) No
Sequential Function Chart (SFC) Yes
(1)
(1) Only affects embedded Structured Text.
5580/5380 Controllers 5570/5370 Controllers