The SCADAPack Modbus driver typically scans each contiguous group of points for data at a particular retrieval interval. The driver calculates the group at the start of the poll, based on the points for which data needs retrieving. Each group comprises a particular address range, for example, holding registers, or input registers. In some instances, there may be gaps in the point Addresses within the group of points that the driver is to scan. This could occur, for instance, if it is not possible or practical to group the data points into tight contiguous point Address ranges.
In such a situation, it may be preferable to scan a wider range of points in a single scan, rather than split those points into smaller scan groups, using the gap in point Addresses to separate each group. A single scan is more efficient if the overhead of making multiple requests outweighs the extra unused bytes in a single read request.
Use the Scanning Gaps section on the SCADAPack tab to specify how Geo SCADA Expert determines the maximum Address gap size before splitting a read request (see Specify how any Scanning Gaps are Handled in the Geo SCADA Expert Guide to the Advanced Modbus Driver).
Further Information
The Type of Calculation that the Driver Performs.
The types of Geo SCADA Expert points that represent Modbus registers, coils, and discretes: see SCADAPack Point Addressing.
The maximum number of registers that can be read in one request: see Modbus Function Codes Supported by the Geo SCADA Expert SCADAPack Modbus Driver.