User Manual

129 Chapter 6
6.3 Modbus Protocol for ADAM-6000 Modules
ADAM-6000 can accept a command/response form with the host com-
puter. When data is not transmitted the modules will be in the listen
mode. The host issues a command to a system with a specified address
and waits a certain period of time for the system to respond. If there's no
response detected, a time-out aborts the sequence and returns control to
the host. This chapter explains the structure of the commands with Mod-
bus/TCP protocol, and you can refer to the example codes provided by
.NET class library to see how to write or read Modbus/TCP address of
ADAM-6000 modules. You can find WinCE, Win32 example at Pro-
gram Files\Advantech\AdamApax.NET Class Library\Sample
Code\ADAM
Note: Please refer to Appendix B.2 for the Modbus/TCP address of
ADAM-6000 modules.
6.3.1 Modbus Protocol Structure
It is important to understand the encapsulation of a Modbus request or
response carried on the Modbus/TCP network. A complete command is
consisted of command head and command body. The command head is
prefixed by six bytes and responded to pack Modbus format; the com-
mand body defines target device and requested action. Following exam-
ple will help you to realize this structure quickly.