Chapter 3. Program DataGFK-2950C February 2018 553.10 User Defined Types (UDTs)A UDT is a structured data type consisting of elements of other selected data types. Each top-levelUDT element can be one of the following:Top-level UDT Element ExampleSimple data type, except STRING INTAnother UDT, except any in which the current UDTis nested at any level.Note: A UDT cannot be nested within itself.A UDT named UDT_ABC has a top-level element whosedata type is another UDT, named UDT_2.Array of a simple data type LREAL array of length 8.Array of UDTsNote: A UDT cannot be nested within itself.A UDT named UDT_ABC has a top-level element that isan array whose data type is another UDT, namedUDT_row.3.10.1 Working with UDTs1. In Machine Edition, add a UDT as a node under a target inthe Project tab of the Navigator. A UDT will be saved withthe target in which it is used.2. Edit the UDT properties and define the elements in the UDT’sstructure.3. Create a variable whose data type is the UDT. By default,the variable resides in symbolic memory. You can convertthe symbolic variable to an I/O variable by assigning it to anI/O terminal.4. Use the variable in logic.3.10.2 UDT PropertiesName: The UDT’s name. Maximum length: 32 characters.Description: The user-defined description of the UDT.Memory Type: The type of symbolic or I/O variable memory in which a variable of this UDT resides.Non-Discrete: (Default) Word-oriented memory organized in groups of 16 contiguous bits.Discrete: Bit-oriented memory.Notes: You cannot nest a UDT of one memory type in a UDT of a different memory type. Changingthe memory type propagates to existing variables of this UDT only after target validation.Is Fixed Size: If set to True, you can increase the Size (Bytes) value to a maximum of 65,535 bytes tocreate a buffer at the end of the UDT. The buffer is included in the memory allocated to everydownloaded variable of that UDT data type. Use of a buffer may allow RUN Mode store of a UDTwhen the size of the UDT definition has changed. For details, refer to RUN Mode Store of UDTs.If set to False (default), the Size (Bytes) value is read-only and does not include a buffer at the end ofthe UDT.Size (bytes): (Read-only when Is Fixed Size is set to False.) The total number of bytes required tostore a structure variable of the user-defined data type (UDT).Bytes Remaining: (Read-only; displayed if Is Fixed Size is set to True.) The UDT's buffer size; thenumber of bytes available before the actual size of the UDT reaches the value of the Size (bytes)property.
