How to Use Unions in Sysmac Studio
Written by Nick Lim
Updated at March 25th, 2025
What is a Union?
Unions members occupy the same memory location
Modifying one member of a union will affect other members, so care must be taken when using them.
Creating Unions
1. In the Multiview Explorer select Data Types. Then select Union on the menu on the left.
2. Right click in the main edit window and click create new data type
3. Give your union a name and then right click and select create new member
4. Give your member a name a data type then repeat 3 and 4 as necessary
N.B. You can only use primitive data types when creating a union (Bools, Bytes, Words, DWords, LWords)
5. Declare your union as a variable using the Union data type you just created
6. Finally you can access members of the union using the following syntax [variable name] . [member name]
Example Usage
Take for an example we receive the control word 0x0F and we interested in the status of bit 2 and 3.
Breaking this down into binary it would be 0000 1111.
There is however no way of directly comparing to an individual bit in a word built into Sysmac and using a greater than operation would not work as ≥4(0000 0100) would not account for bit 3, ≥8(0000 1000) does not account for bit 2 and ≥C(0000 1100) would not work as 0x10 (0001 0000) is also a possible solution.
However using the union in our previous example you can see we can operate on individual elements in our bit array
