It is possible to display in the Trending Tool a maximum of 16 variables scanned and timestamped at MAST scan time in the PLC. That allows to have the real state of the 16 variables at the PLC time scan. Other variables in Trending Tool are displayed with a time stamping set when the trending function receives the PLC notification.
Adding PLC Timestamped Variables
To add PLC timestamped items:
1
Check Enable fast scanning for trending check box in Variables leaf in Project Settings.
2
For each variable you want to scan by the PLC, check the Scan Variable property in General attributes tab in Data Properties window.
3
Rebuild and download project in the PLC (if necessary).
Using PLC Timestamped Variables
NOTE: To use timestamped variables, the date and time of the PLC must be updated.
Fast scanned variables have the same behaviors than other Trending Tool variables. You can use fast scanned variable with standard variable but not mix them inside the same module.
Fast scanned variables are tag with an icon depending on its type plus
mark. The first variable added to trend module configures it like a fast or a standard module.
Fast modules can only own fast scan variables.Standard modules can only own standard variables.If user tries, an error will appear.
Using PLC Time for Reference
It is possible to choose the reference time to use for time stamping events. You can choose between PLC Time and PC Time.
If you choose PLC Time, Trending Tool reads Real-time clock of the PLC before starting the record and use it as reference time. In this case, check the PLC Real-time clock before recording.
If you choose PC Time, Trending Tool reads Real-time clock of the PC before starting the record and use it as reference time.
By default, PC Time is used as reference.
Limitations are:
1
You cannot mix fast scanned variable with standard variable inside a same module.
2
You cannot fast scanned more than 16 variables.
3
This option is available only on EDT types (except STRING, DT, TOD, TIME and DATE ).
4
This option is not available on Safety CPU, Premium & M340 CPU with version less than V2.9 and Quantum CPU with version less than V3.0.
5
The functionality was designed to be as fast as possible but fast scan get variables values only at MAST periodic time. So if a variable is modified more than one time per MAST cycle, you will only have its value at the end of MAST cycle.
6
If the Mast cycle is very short, it's possible to lose some events. The quality is then considered like bad. In this case red hatching appear in Trending Tool time line.It is necessary to have a minimum duration cycle time upper than 5 ms. In case of CYCLIC period the cycle time is adjust by program.
7
When you mixed fast scanned variables with standard variables in Trending Tool, you can have poor performance on standard variables if the mast period is short.
8
The trending of fast scanned variables need to connect Control Expert and PLC via USB or Ethernet link.
9
The trending of fast scanned variables is only available if the MAST task is configured as a periodic task, not as a cyclic task. 
