I/O Address Format
OpenPLC uses a particular format for binding variables to addresses. It took a bit of digging around, but I’ve finally figured out what they mean and how OpenPLC interprets the addresses. The first part is to define a general identification for types:
| Data Width | Input | Output | Memory |
|---|---|---|---|
| Bit | IX |
QX |
MX |
| Byte | IB |
QB |
MB |
| Word | IW |
QW |
MW |
| Double word | ID |
QD |
MD |
| Long word | IL |
QL |
ML |
Items with a strike-through are not currently supported. There is another important note. These values should indicate the data width (not the type). However, as far as I can tell, OpenPLC assumes data types based on the definitions, which means you don’t have freedom to use they as containers.
(I’m not 100% sure that my understanding of IEC 61131-3 is correct since I only have a book rather than the original specification).