Is there any way to define a single Item to address a block of V-memory?
Unfortunately this is not possible with DSData and the ECOM. It was an engineering decision given the then pros and cons. There must be a one-to-one correspondence between PLC data types and OPC/DDE reference types. So the problem begins with the fact that there’s no block (or array) data type in the Direct Logic (DL) PLCs sold by Automation Direct. Without this data type in the PLC, there’s no way for any DDE/OPC client to create an Item that can reference a range of data in the PLC. However, each read that you request from DSData is grouped automatically by DSData whenever it can. In other words, when you do reads of contiguous V-memory locations, DSData groups them into one read for the communications server (CommServer; CSMAIN) and they are read from the PLC as fast as possible. Once the data is gathered in this manner, DSData then separates this block of data into the individual Items.
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