384 Fieldbus control through the embedded fieldbus interface (EFB)Modbus function codesThe table below shows the Modbus function codes supported by the embeddedfieldbus interface.Code Function name Description01h Read Coils Reads the 0/1 status of coils (0X references).02h Read Discrete Inputs Reads the 0/1 status of discrete inputs (1Xreferences).03h Read Holding Registers Reads the binary contents of holding registers (4Xreferences).05h Write Single Coil Forces a single coil (0X reference) to 0 or 1.06h Write Single Register Writes a single holding register (4X reference).08h Diagnostics Provides a series of tests for checking thecommunication, or for checking various internal errorconditions.Supported subcodes:• 00h Return Query Data: Echo/loopback test.• 01h Restart Comm Option: Restarts and initializesthe EFB, clears communications event counters.• 04h Force Listen Only Mode• 0Ah Clear Counters and Diagnostic Register• 0Bh Return Bus Message Count• 0Ch Return Bus Comm. Error Count• 0Dh Return Bus Exception Error Count• 0Eh Return Slave Message Count• 0Fh Return Slave No Response Count• 10h Return Slave NAK (negative acknowledge)Count• 11h Return Slave Busy Count• 12h Return Bus Character Overrun Count• 14h Clear Overrun Counter and Flag0Bh Get Comm EventCounterReturns a status word and an event count.0Fh Write Multiple Coils Forces a sequence of coils (0X references) to 0 or 1.10h Write Multiple Registers Writes the contents of a contiguous block of holdingregisters (4X references).16h Mask Write Register Modifies the contents of a 4X register using acombination of an AND mask, an OR mask, and theregister’s current contents.17h Read/Write MultipleRegistersWrites the contents of a contiguous block of 4Xregisters, then reads the contents of another group ofregisters (the same or different than those written) ina server device.
