Control through the embedded fieldbus interface 337
Modbus function codes
Table below shows the Modbus function codes supported by the embedded fieldbus
interface.
Code Function name Description
0x03 Read Holding Registers Reads the contents of a contiguous block of holding
registers in a server device.
0x06 Write Single Register Writes a single holding register in a server device.
0x08 Diagnostics Provides a series of tests for checking the
communication between the master and the slave
devices, or for checking various internal error
conditions within the slave. The following subcodes
are supported:
• 00 Return Query Data:
The data passed in the request data field is to be
returned in the response. The entire response
message should be identical to the request.
• 01 Restart Communications Option:
The serial line port of the slave device must be
initialized and restarted, and all of its communication
event counters cleared. If the port is in the Listen Only
mode, no response is returned. If the port is not in the
Listen Only mode, a normal response is returned
before the restart.
• 04 Force Listen Only Mode:
Forces the addressed slave device to the Listen Only
mode. This isolates it from the other devices on the
network, allowing them to continue communicating
without interruption from the addressed remote
device. No response is returned. The only function
that will be processed after this mode is entered is the
Restart Communications Option function (subcode
01).
0x10 Write Multiple Registers Writes the contents of a contiguous block of holding
registers in a server device.
0x17 Read/Write Multiple
Registers
Writes the contents of a contiguous block of holding
registers in a server device, then reads the contents
of a contiguous block of holding registers (same or
different than those written) in a server device.
0x2B/0x0E Encapsulated Interface
Transport / Read Device
Identification
Allows reading of identification and other information
of the server.
Parameter "Read Device ID code" supports one
access type:
01: Request to get the basic device identification.
Returns ABB,ACS850.
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