IGS-NT Communication Guide
40
Modbus/TCP access code
Every Modbus/TCP session has to be started with writing the access code from the modbus/tcp client to the
controller. If the session is closed and reopened again the access code must be written again. The session can
be closed by the client or the controller closes the session automatically if there is no activity from the client
side for 15s.
There are new dedicated registers for entering the AccessCode via Modbus/TCP.
The register numbers are 46339-46346 (register address 6338-6345).
The previous method using register address 24535 remains working as well.
Example of the Modbus message is following (in HEX):
01 10 18 C2 00 08 10 30 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 FE F3
01 Controller address
10 Modbus function (16dec – Write multiple registers)
18C2 Register address (18C2hex = 6338dec = register 46339)
0008 Number of registers
10 Length of the data (Number of registers x 2B)
30000000... Access code string (16 chars, null-terminated, ASCII, here “0”)
FEF3 CRC
Some devices do not support the modbus function 16. In this case can be the access code writen in controller
as one register No. 46339 using the function 6. The access code has to be the number in the range 0 to 65535.
Equipment
Equipment needed
Controllerside -
Connection
Ethernet cable (page 85) to LAN, for point to point connection between PC and
controller use cross-wired cable
PC side ETHERNET connection
For more informations about ModBus implementation to ComAp controllers see Modbus Communication on
page 90.
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