Device Addressing; Supported Modbus Functions; Function Descriptions; Table 26. Supported Modbus Functions - WEST P8700 User Manual

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Device Addressing

The instrument is assigned a unique device address by the user in the range 1 (default) to
255 using the 5DD9 parameter in Configuration Mode. This address is used to recognise
Modbus Queries intended for this instrument. The instrument does not respond to Modbus
Queries that do not match the address that has been assigned to it.
The instrument will also accept global Queries using device address 0 no matter what device
address is assigned. No responses are returned for globally addressed Queries.

Supported Modbus Functions

Modbus defines several function types; these instruments support the following types:
Function
Code
(decimal)
01 / 02 Read Coil/Input Status
03 / 04 Read Holding/Input registers
05 Force single Coil
06 Pre-set Single Register
08 Diagnostics
16 Pre-set Multiple Registers

Function Descriptions

The following is interpreted from the Modbus Protocol Description obtainable from
http://www.modicon.com/ or http://www.modbus.org/. Refer to that document if clarification is
required.
In the function descriptions below, the preceding device address value is assumed, as is the
correctly formed two-byte CRC value at the end of the QUERY and RESPONSE frames.
59305, Issue 5 – March 2005
- DIN Controllers & Indicators - Product Manual

Table 26. Supported Modbus Functions

Modbus Meaning Description
Read output/input status bits at given address.
Read current binary value of specified number
of parameters at given address. Up to 64
parameters can be accessed with one Query.
Writes a single binary bit to the Specified Slave
Bit address.
Writes two bytes to a specified word address.
Used for loopback test.
Writes up to 1 word parameter values to the
specified address range.
Modbus Communications Page 95