Device/group-specific parameters

The MODBUSA driver can apply different initialization parameter values to specific I/O devices or groups of I/O devices. This means the user can specify:

• Global parameters that apply to all devices.

• Channel- (port-) level parameters that apply to all devices on the specified port.

• Group-level parameters that apply to all devices in a specified group.

• Device-level parameters that apply only to the specified device.

Note: Always seek the advice of Technical Support personnel for this product regarding undocumented features.

This feature can be implemented in the citect.ini for the following MODBUSA Parameters:

• Broadcast

• BroadcastDelay

• FloatMode

• ForceMultiCoilsOnly

• InitType

• InitUnitAddress

• LongDataType

• PresetMultiRegistersOnly

• RegisterBitReverse

• SendBCDSwap

• StringReverse

To set parameters for a particular port, group, or device, you must create a new section in the citect.ini file. Label it with the driver name followed by a period (.) character and the name of the particular port, group, or device you want to specify the parameter setting for.

For example:

• [MODBUS.<Port_Name>]: applies the parameter settings to the specified port.

• [MODBUS.<Group_Name>]: applies the parameter settings to the specified group.

• [MODBUS.<Port_Name>.<IODevice_Name>]: applies to the specified device.

Any parameters you then define in the following section of the citect.ini file relate only to the specified device or device group.

Example

The following citect ini file format is an example of how the InitType parameter could be specified differently for different I/O devices communicating using the Modbus protocol.

Assume that two ports are used: PORT1 and PORT2.

PORT1 has three I/O devices attached:

• DEV1A DEV1B EV1C

PORT2 also has three devices:

• DEV2A DEV2B DEV2C

Assume that the user has specified that DEV1C and DEV2C belong to GROUPZ. The citect.ini file contains the following entries:

[MODBUS]
InitType=1
[MODBUS.PORT1]
InitType=2
[MODBUS.PORT2]
InitType=2
[MODBUS.GROUPZ]
InitType=3
[MODBUS.PORT1.DEV1A]
InitType=1
[MODBUS.PORT2.DEV2B]
InitType=4

The resultant InitType for the I/O devices will be as follows:

As the above example shows, there is a hierarchy that determines the outcome of such settings. In simple terms, specific parameter settings overwrite general level settings. Therefore, parameters written in the scope of I/O devices will overwrite those set for groups; parameters set for groups will overwrite global settings, and so on.