Addressing Bits

In order to address individual bits in Ignition, you must create a separate OPC tag pointing directly to the specific bit in the PLC.

When the integer values that come from the OPC tags are a series of binary bits, it is then possible to address each bit. For example, an integer value can have a 16-bit binary representation as shown here:

Integer
Bit level representation
How it works

4096

0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0

212 = 4096

1025

1,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0

20 + 210 = 1025

To address an individual bit

Suppose a MicroLogix PLC is connected to a Gateway.

  1. From the Tag Editor window, create an OPC tag to have:
    Data Type: Integer with a value of 1025
    OPC Item Path: [MLX]B3:0

  2. Then create a new OPC tag with a Boolean value to the first bit of this tag as follows:
    Data Type: Boolean with a value of 1 or True
    OPC Item Path: [MLX]B3:0/0 (for Micrologic, you can specify the bit as: 0/0 or 0.0. That is, with a slash/ or a period.) [MLX]B3:0/0 has a value of 1 or a Boolean value of True

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