isoNAV685-D_D00215_02_M_XXEN/04.2017
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Modbus settings
18. Modbus settings
18.1 General information
This appendix provides a complete description of the Modbus register (protocol version 6.0)
for the ISOMETER® iso685 family of devices to facilitate access to information.
The adjustable parameters for individual keys are listed.
In general, the Registers are implemented as Modbus read-only register (RO = read only).
An exception is the DO control register, which only has a write function (WO = write only).
The ISOMETER® iso685 device family supports 4-digit addressing and the following Mo-
dbus functions:
4. Holding registers for reading values
(Read Holding Register; function code 0x03)
5. Registers for device programming
(Preset Multiple Registers; function code 0x10)
For the complete Modbus protocol specification, visit
http://www.modbus.org.
18.2 Data access by means of Modbus/TCP-Protokoll
Requests to the iso685 Modbus/TCP-Server are carried out using the Function code FC4
(read input registers). The server generates a function-related response and sends it to
the Modbus client.
Maximum of Modbus TCP requests per second: 100/s.
18.2.1 Exception code
If a request cannot be answered for whatever reason, the server sends a so-called excep-
tion code to limit possible errors.
18.2.2 Modbus request
By means of the function code FC3, the required information, in Words, can be read from
the ISOMETER® iso685 input registers. To enable this, the start address and the number of
registers to be read must be specified.
Example:
The insulation value should be read from the input register with a start address of 0x2000.
Exception-Code
Description
0x01
Invalid function
0x02
Invalid data access
0x03
Invalid data value
0x04
Slave device error
0x05
Acceptance confirmed (response is delayed)
0x06
Request not accepted (repeat request if necessary)
0x08
Memory: Parity error
0x0A
Gateway path not available
0x0B
Gateway Error
Byte
Name
Example
Byte 0,1
Transaction identifier
0x0000
Byte 2,3
Protocol identifier
0x0000
Byte 4,5
Length field
0x0006
Byte 6
Unit identifier
BCOM device address
Byte 7
Modbus function code
0x03
Byte 8,9
Register address defined in “Mod-
bus register assignment” on page
0x2000
Byte 10,11
Number of Words
0x0002
