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As shown in the figure 46, the general Modbus TCP data flow direction is (1)
(2)
(3)
(4). First, the Modbus TCP command is transformed into the corresponding instruction
of Modbus RTU, and then the device responds Modbus RTU instruction to Modbus
gateway, and then Modbus gateway is converted again to Modbus TCP to be sent to the
monitoring upper computer.
We know that Modbus TCP is a network communication, and the transmission speed is
very fast. Generally, it can be answered in 3ms, while Modbus RTU is RS485, which
generally only has a speed of 9600bps, and generally sends and returns an instruction at
least 30ms. This common non-storage Modbus gateway has a longer query response
time. In addition, if there are a lot of upper computer at the same time to query the data,
then the serial port will be congested. If the network is compared to a highway, the serial
port is a foot-bridge, then the original way is to carry the highway traffic on the
foot-bridge.
The storage Modbus gateway solves these problems. It can query for the register data
temporarily stored in the Modbus gateway inside, so the Modbus TCP queries, Modbus
gateway can immediately return instructions, really the features of the Modbus TCP
quick play out. On the other hand, the saved Modbus gateway can automatically update
the contents of the current saved register data by sending instructions automatically from
the serial port, and keep a new register value.
The storage Modbus gateway ZLAN5143 is a fully automatic Modbus gateway with no
configuration required. The user does not need to configure the required register address,
function code, slave station address and so on. ZLAN5143 will automatically identify and
dynamically add these registers.
ZLAN5143 can show a good reaction speed in multiple computer monitoring, regardless
of the baud rate of serial port, it is generally able to give the upper response data within
3ms. It also shows the speed of real-time update of serial data.
Register storage Modbus gateway is the real Modbus TCP to Modbus RTU, which really
gives full play to the advantages of fast speed, multi-host simultaneous query of Modbus
TCP.