Figure 48: Supervisory
Timer Selection

ICC

10.10.2 Supervisory Timer Selection

Figure 48 shows the checkbox which enables the interface card’s Modbus “supervisory timer” function. This timer provides the ability for the interface card to monitor timeout occurrences between successive Modbus TCP socket connections, as opposed to the standard timeout functionality (refer to section 10.7.5), which monitors timeout occurrences only within the

scope of each client socket connection. While this feature provides an additional level of fail-safe functionality for those applications that require it, there are several ramifications that must be understood prior to enabling this capability. Before enabling this timer, therefore, it is suggested that users read the ICC whitepaper titled “A Discussion of Modbus/TCP Server-Side Timeout Processing”, which can be found in the documents section at http://www.iccdesigns.com.

10.10.3 Register Remap Configuration

At times, it may be convenient to access inverter registers in bulk Modbus transactions. This may be especially true in situations where it is desired to access certain registers that are natively non-contiguous. For example, if it were desired to read the inverter’s status 1 word (register 1302), torque (register 1319) and output voltage (register 1306), this could be accomplished in two different ways:

1.Implement three separate Modbus read transactions, each one reading one register only, or

2.Implement one single Modbus read transaction, starting at register 1302 for a quantity of 18 registers. Then, pick out the registers of interest and ignore the rest of the response data.

While both of these methods will certainly work, neither one of them is optimized for the task at hand, which is to access three specific register values. A fully optimized solution can be realized, however, by making use of the interface card’s Modbus register remapping capabilities. This mechanism operates by allocating a block of 50 user-configurable registers (2001..2050) that remap to other inverter registers. In this way, non-contiguous inverter registers can be grouped together in any order and accessed efficiently via the Modbus TCP “read multiple registers” and “write multiple registers” function codes. The net effect is one of being able to transfer larger blocks of registers using fewer Modbus transactions, which results in improved network utilization and simpler data manipulation code on the Modbus master device.

Figure 49 shows the register remap configuration array. Clicking on an entry field in the “Remaps To” column allows the user to enter an inverter register number that will then be accessible at the register indicated in the adjacent “Register” column. An assignment of 0 in the “Remaps To” column indicates that no inverter register is remapped at that location, which results in written values being ignored and read values returned as a default value of 0. Note that remapped inverter registers are still accessible at their original locations: remapping simply provides an additional means of accessing the original register’s value.

49