Specifications

STB NIP 2311 Services
EIO0000000051 6/2010 137
Modbus Commands Supported by the STB NIP 2311 NIM
Introduction
The Modbus protocol describes the process that a controller uses to access another
device, how that device responds, and how events are detected and reported. (For
detailed information on the Modbus protocol, see www.mobus.org.)
Modbus Message Data Frame
Modbus messages are embedded within the frame or packet structure of the
network in use. A Modbus over TCP/IP network uses either the Ethernet II or
IEEE 802.3 data formats. For communications with the STB NIP 2311 NIM, Modbus
messages can be embedded in either frame type. (Ethernet II is the default data
format.)
Modbus Message Structure
The Modbus protocol uses a 16-bit word. A Modbus message begins with a header.
The first byte of the message uses a Modbus function code (see page 137).
Following is a description of the structure of a Modbus message header:
List of Supported Commands
The following table lists the Modbus commands that the STB NIP 2311 NIM
supports:
Invoke Identifier Protocol Type Command Length Destination ID Modbus Message
2-byte field that
associates a request
with a response
2-byte field
value for Modbus is
always 0
2-byte field
value is the size of the
rest of the message
1-byte n-byte field
first byte is the Modbus
function code
Modbus
Function Code
Subfunction
or Subindex
Command Valid Range Max. No. of Words
per Message
3 read holding registers (4x) 1...9999 125
4 read input registers (3x) 1...4697 125
6 write single register (4x) 1...5120 and 9488...9999 1
8 22 get/clear Ethernet statistics
(see page 138)
0...53 N/A
16 write multiple registers (4x) 1...5120 and 9488...9999 100
22 mask write registers (4x) 1...5120 and 9488...9999 1
23 read/write multiple registers (4x) 1...5120 and 9488...9999 100 (write)
1...9999 (read) 125 (read)