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as “rd_reg_1301[4]”, which starts at register 1301+4 = register 1305, the drive’s input voltage monitor register).
In a similar manner, to write data to the interface card, the application PLC program must reference a “destination element” to which to start writing and the “number of elements” to write. Again, the “destination element” will be a tag name constructed according to the naming convention shown above, or a special tag as shown in Table 4.
Whether reading or writing, the “number of elements” can be any quantity of registers from 1 to the maximum allowable length (1485).
13.2.6 ControlLogix Example: Read a Register Block
This example program will show how to continuously read a block of registers from the drive with a single MSG instruction. Only one read request is outstanding at any given time.
1)Create new Tags.
a)Double click “Controller Tags” in the controller organizer view.
b)The “Controller Tags” window appears. Refer to Figure 72.
Figure 72: Create New Tags
c)Select the “Edit Tags” tab at the bottom.
d)Create a new tag by entering “connection” in the first blank Name field, and change its Data Type to “MESSAGE”. This tag will contain configuration information for the MSG instruction.
e)Select the “Monitor Tags” tab. Expand the “connection” tag by clicking on the “+” sign next to the tag name. Scroll down to the connection.UnconnectedTimeout field and change its value from the default 30000000 (30s in 1uS increments) to 1000000 (1s). This value determines how long to wait before timing out and retransmitting a connection request if a connection failure occurs. Refer to Figure 73.
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