Register Mappings Guidelines

This sectionprovides the user with guidelines for defining register mappings.

Guideline to Organize Records

The register mappings (and other types of records) may be specified in any order. To simplify maintenance of the configuration file, order the register mapping records by slave address then register reference. This will aid in detecting unmapped data addresses.

Since the Modbus RTU Slave Interface can emulate multiple Modbus RTU Slave devices, one could organize mapped CIMPLICITY points into logical groupings based on a functional area.

Guideline to Optimize Throughput

The Modbus RTU Slave Interface supports several Modbus requests that allow a range of data addresses (or an array of values) to be specified. Note that these requests specify a contiguous set of data addresses.

To maximize throughput, avoid gaps in allocated data addresses. This will reduce the transfer of "meaningless" values.

In addition, map Boolean points to coil (0X) or input status (1X) data addresses. Modbus requests that handle coil or input status data addresses pack sixteen (16) values into one word (two bytes). Modbus requests that handle input register or holding register data addresses require one word per value.

Another way to maximize throughput is to allow the Modbus master to reduce the number of transactions by increasing the range of data addresses in each request.

More information

Limits on the number of coils or registers that may be specified or included in a single Modbus message.

Further details on how the behavior of the Modbus RTU Slave Interface can affect configuration decisions.

Step 1. Edit the Modbus RTU Slave configuration file.