Starting in AX-3.5 and later (or build 3.4.52 or higher), support was added for Modbus function code 07 (read Exception Status). A related component is now on the palette of Modbus client drivers (modbusAsync, modbusTcp): ModbusClientExceptionStatus, as shown in Figure 38.

Usage is “per device”, where you copy (drag) from the palette, and paste (drop) directly onto a client Modbus device —it must be a direct child of the ModbusAsyncDevice, ModbusTcpDevice, or ModbusTcpGatewayDevice.

Slots in this component include a “Bytes Returned” configuration property, where you specify whether the device uses 1 or 2 bytes for exception status, and also the poll frequency to be used. Read-only “Read Status” properties provide a numeric “Error Code” and “Error Description”, as well as timestamps of both the last successful and last failed read attempts.

Other output slots expose the exception status data as StatusBooleans on “Bit0” to “Bit15”, as well as a StatusNumeric “Out” slot.

Implementation of function code 07 (read Exception Status) varies among devices, but often is at least one returned byte that maps bits to various “unit status” information. For example, a vendor’s Modbus standby generator interface may respond to a function code 07 request with a byte of the following bitmapped data (as applied to any bit that is set):

Refer to the vendor’s documentation for a Modbus device to see if/how function code 07 is supported.