Rockwell Automation Logix5000 Controllers Add-on Instructions Programming Manual - Manual (Page 35)

Designing Add-On Instructions Chapter 1
Constant values
InOut parameters may be designated as constant value tags to prevent their data
from being modified by controller logic. If the logic of an Add-On Instruction
contains a write operation to a constant value parameter, the Add-On Instruction
does not verify in the Add-On Instruction definition context.
External Access
External Access defines the level of access that is allowed for external devices, such
as an HMI, to see or change tag values.
Add-On Instruction Parameters and Tags External Access Options
Local tag
Read/Write
Read Only
None
Input parameter
Output parameter
EnableIn parameter
Read Only
EnableOut parameter
InOut parameter
N/A
Rock well Automati on Publication 1756- PM010F-EN-P - Oct ober 2014 35