Rockwell Automation 1756-OF8H ControlLogix HART Analog I/O Modules - Manual (Page 146)

146 Rockwell Automation Publication 1756-UM533C-EN-P - February 2011
Chapter 10 Unlatch Alarms and Reconfigure Modules By Using Ladder Logic
Processing Real-time Control and Module Services
Services sent via message instructions are not as time critical as the module
behavior defined during configuration and maintained by a real-time connection.
Therefore, the module processes messaging services only after the needs of the
I/O connection are met.
For example, you want to unlatch all process alarms on the module, but real-time
control of your process is still occurring using the input value from that same
channel. Because the input value is critical to your application, the module
prioritizes the sampling of inputs ahead of the unlatch service request.
This prioritization lets input channels be sampled at the same frequency and the
process alarms be unlatched in the time between sampling and producing the
real-time input data.
One Service Performed Per Instruction
Message instructions cause a module service to be performed once per execution.
For example, if a message instruction sends a service to the module to unlatch the
high high alarm on a particular channel, that channel’s high high alarm unlatches,
but can be set on a subsequent channel sample. The message instruction must
then be re-executed to unlatch the alarm a second time.
Creating a New Tag
Do these steps to create a new tag by writing ladder logic in the Main Routine.
1. Double-click on MainRoutine (which might require expanding the
MainProgram by clicking the ‘+’ sign).