User manual

Chapter 6
Planning Your Application Program
6-3 ADAM-5000/TCP Command
ADAM-5000/TCP system accepts a command/response form with the
host computer. When systems are not transmitting they are
in listen mode. The host issues a command to a system with a
specified address and waits a certain amount of time for the
system to respond. If no response arrives, a time-out aborts the
sequence and returns control to the host. This chapter explains
the structure of the commands with Modbus/TCP protocol, and
guides to use these command sets to implement user’s programs.
6-3-1 Command 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 command body defines
target device and requested action. Following ex- ample will help you
to realize this structure quickly.
Example:
If you want to read the value of ADAM-5017 in ADAM-5000/TCP’s slot
0(2 channels; address: 40001~40002), the request command should be:
Figure 6-1: Request Comment Structure
6-32 ADAM-5000/TCP User’s Manual