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Allen-Bradley
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SLC 500 Tag Variables for DH485 Protocol
The following chart lists the legal tag variable names that can be used with the SLC 500 series. The
target display talks to the SLC500 using the DH485 protocol. The DH485 protocol requires each
device to have a node address. The Source ID is the target display node address and the Destination ID
is the node address for the SLC. (See the "Setup for using an AB SLC 500 PLC" section for details
about entering the source and destination ID's).
When there is a single point connection between a target display and a SLC500, the destination ID
(node address for SLC) becomes the default address for all variables. That is, if you use the tag variable
N7:100, the target display knows that this variable is located at the destination node address.
When the target display is connected to a DH485 network that includes multiple SLC nodes, there is an
optional variable naming element that will allow you to read information from any SLC node. The
additional element is _D, where the underscore D indicates a node address other than the Destination
ID node address.
In this example, the Source ID (target display address) has been set to 0 and the Destination ID (SLC
node address) has been set to 1. There is an additional SLC on the DH485 network located at node
address 3. To read information from node address 1, the variable would be N7:100. Remember that the
Destination ID is the default node address. To read information from node address 3, the variable
would be N7:100_3. The general format for tag variables is shown below.
N7:100/00_D
Destination Node Address
Bit Address
Element
File Type
SLC 500 Tag Variables for DH+ Protocol
The DH+ tag variables are the same as the PLC5 tag variables except for the following items.
1. You cannot read or write Input (I) or Output (O) variables in the SLC 5/04.
2. The SLC 5/04 can read/write string variables (ST) while the PLC 5 cannot.
