User manual

Some additions to the MODBUS protocol have been made according to the network
structure in the MODBUS/TCP protocol. An example of a MODBUS/TCP data packet is
given in Figure 2. As you can see, there is an MBAP header in the packet structure. The
explanations of the data blocks are given in Figure 2.
Figure 2. Modbus Packet Structure
Query Number
MODBUS protocol is a request/response based protocol. It means that which response
belongs to which request is already defined when the first request is created. The information
requested by the client in the Nth packet is sent as the Nth response packet by the server. Let's
imagine a scenario like below to comprehend the importance of the query number for the
communication over the internet.