ExDesc (extended descriptor)

Depending on the version of the PI API and the Data Archive, this Interface supports an ExDesc attribute whose length is at most 80 or 1023 characters. The following table indicates the maximum length of this attribute for all the different combinations of PI API and Data Archive versions.

If the Data Archive version is earlier than 3.4.370.x or the PI API version is earlier than 1.6.0.2, and you want to use a maximum ExDesc length of 1023, you need to enable the PI SDK.

The extended descriptor can be used to specify additional and optional attributes such as a trigger tag (for input tags only), a bit mask (for input tags only), a custom data type manipulator, an instrument zero value for a PLC and byte swapping.

Use the following syntax for the extended descriptor:

event=’triggertag’,b=bitmask,c=cdtm,z=InstZero,solitary,swap

For example:

event=’sinusoid’,b=01,c=3,z=10,swap

The trigger tag, bitmask, custom data type manipulator, instrument zero and byte swapping descriptors must be separated by commas. The following subsections describe the format and usage of each of the extended descriptors:

Note: For backward compatibility to versions prior to 4.x, the ExDesc attribute may contain metadata that is not one of the ExDesc attributes listed below.

The ExDesc attribute cannot include spaces. Any attributes listed after a space will be ignored.