Hostname

The Hostname value is the IP Address of the Modbus device.

Communication Timeout

After sending a request to the Modbus device, the Communication Timeout setting is the amount of time in milliseconds to wait for a response before treating it as a failure.

TCP Port

The TCP port to use when connecting to a Modbus device. The Modbus TCP port specified in the Modbus specification is 502, but it can be changed to a different port.

Maximum Holding Registers per Request

Some Modbus devices cannot handle the default of requesting 125 Holding Registers in one request. To accommodate this limitation change this setting to the maximum number of Holding Registers the device can handle.

Maximum Input Registers per Request

Some Modbus devices cannot handle the default of requesting 125 Input Registers in one request. To accommodate this limitation change this setting to the maximum number of Input Registers the device can handle.

Maximum Discrete Inputs per Request

Some Modbus devices cannot handle the default of requesting 2000 Discrete Inputs in one request. To accommodate this limitation change this setting to the maximum number of Discrete Inputs the device can handle.

Maximum Coils per Request

Some Modbus devices cannot handle the default of requesting 2000 Coils in one request. To accommodate this limitation change this setting to the maximum number of Coils the device can handle.

Use Zero Based Addressing

The Modbus specification states that Modbus addresses are to be zero based. Meaning Modbus addresses start at 0 instead of 1 and to read a value from Modbus address 1024, 1023 is sent to the device. When connecting to devices that do not adhere to zero based addressing, make sure this option is not selected. This will cause 1024 to be sent to the device to read Modbus address 1024.

Reverse Numeric Word Order

When reading and writing 32bit values from/to a Modbus device, the low word comes before the high word. By checking this option, the high word will come before the low word. The Modbus specification does not include a section for reading and writing 32bit values and as a result device manufacturers have implemented both methods.

Reverse String Byte Order

When reading and writing string values from/to a Modbus device, the low byte comes before the high byte. By checking this option the high byte will come before the low byte. If reading a string value from a device should read ABCD but BADC appears in Ignition then check this option.

Right Justify Strings

Strings stored in a Modbus device may contain leading spaces or trailing spaces. This can produce unwanted results so that Modbus driver removes spaces or zeros when reading string values. By default, left justify string handling will be used when reading and writing strings. By checking this option, right justify string handling will be used.