Device Point Properties

On the Device tab in the Point Properties dialog box, the following fields have special meaning for the Modbus RTU Communications option:

Update Criteria

The update criteria you select determines how the data will be requested.


Select On Scan or On Change for points whose values should be polled by Modbus RTU communications at regular intervals.

Select On Demand On Scan or On Demand On Change for points whose values should be polled by Modbus RTU communications at regular intervals while users are viewing them..


Enter the point address of the data as follows:

0xxxx or 0xxxxx for Coils

1xxxx or 1xxxxx for Discrete Inputs

3xxxx or 3xxxxx for Input Registers

4xxxx or 4xxxxx for Holding Registers

6yxxxx or 6yxxxxx for General Reference

D4xxxx or D4xxxxx for Holding Registers as Double Precision. For the 3270 ACM meter, this address represents a register whose value is expressed in mod 10000 format.


where xxxx or xxxxx is the bit number or register number of the point. For example, the address of Holding Register one is 40001 and the address of Coil one is 00001.


If you are configuring a General Reference point, the file number is y.


Double Precision points in Holding Registers require two Holding Registers per point. The upper register is multiplied by 10000 and the product is added to the lower register to get the resulting value. No more than one Double Precision point may be written in a single write operation. Use DINT or UDINT types for these points.


If you are configuring an Analog point type in Discrete Inputs or Coils, the address entered in this field must be that of the least significant bit of the point.

For example, to configure a 16-bit analog point for Coils 17 through 32, enter 00017 in this field.

When you configure Boolean points in Holding Registers, Input Registers, or General Reference, you must also enter data in the following field:

Bit Offset

Enter the bit offset in the Holding Register, Input Register, or General Reference that defines the point, where 0 is the least significant bit and 15 is the most significant bit.

More information

Modbus RTU point configuration.