Tag Configuration Optimization Since the interface will assemble related tags with contiguous data offsets into groups in order to maximize the number of tag values requested in a single Modbus write command, it is best for the user to configure related tags in a manner in which tag groups can be leveraged to minimize the number of requests to write the tag data. In other words, the more related tags whose data offsets are contiguous, the better. NOTE: In some cases it may necessary that an output tag within a group of contiguous tags have a source tag dependency that will have a detrimental effect on the timely update of all of the tags in the group. In that case the output tag can excluded from optimization by use of the descriptor in the attribute of the tag. For example, assume that a user creates 200 tags with the attribute values specified in the following table: Point Attribute Description Value Instrument Tag Ethernet node COM3 Location 2 PLC Node 2 Location 3 Write multiple registers containing 16-bit integer 116 Example 1 If the 200 tags have data offsets of 1 to 40, 51 to 90, 101 to 140, 151 to 190 and 201 to 240 respectively, the tags will be represented by five tag groups. The following table represents the five tag groups and the consecutive offsets in each group: Tag Group Tag Offsets 1 1 to 40 2 51 to 90 3 101 to 140 4 151 to 190 5 201 to 240 In this case five requests will have to be made to write the values for the 100 tags. Example 2 If the 200 tags have data offsets of 101 to 300, the tags will be represented by two tag groups: tag groups 1 and 2. The following table represents how the tags will be located in the two groups: Tag Group Tag Offsets 1 101 to 223 2 224 to 300 In this case two requests will have to be made to read the values for the 100 tags since the maximum number of values in a single write request is 123.
Tag Configuration Optimization Since the interface will assemble related tags with contiguous data offsets into groups in order to maximize the number of tag values requested in a single Modbus write command, it is best for the user to configure related tags in a manner in which tag groups can be leveraged to minimize the number of requests to write the tag data. In other words, the more related tags whose data offsets are contiguous, the better. NOTE: In some cases it may necessary that an output tag within a group of contiguous tags have a source tag dependency that will have a detrimental effect on the timely update of all of the tags in the group. In that case the output tag can excluded from optimization by use of the descriptor in the attribute of the tag. For example, assume that a user creates 200 tags with the attribute values specified in the following table: Point Attribute Description Value Instrument Tag Ethernet node COM3 Location 2 PLC Node 2 Location 3 Write multiple registers containing 16-bit integer 116 Example 1 If the 200 tags have data offsets of 1 to 40, 51 to 90, 101 to 140, 151 to 190 and 201 to 240 respectively, the tags will be represented by five tag groups. The following table represents the five tag groups and the consecutive offsets in each group: Tag Group Tag Offsets 1 1 to 40 2 51 to 90 3 101 to 140 4 151 to 190 5 201 to 240 In this case five requests will have to be made to write the values for the 100 tags. Example 2 If the 200 tags have data offsets of 101 to 300, the tags will be represented by two tag groups: tag groups 1 and 2. The following table represents how the tags will be located in the two groups: Tag Group Tag Offsets 1 101 to 223 2 224 to 300 In this case two requests will have to be made to read the values for the 100 tags since the maximum number of values in a single write request is 123.
PI_ModbusE_4.0.2.80.docx