USR-M511User Manual Technical Support:
h.usriot.com
Jinan USR IOT Technology Limited
www.usriot.com
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2.2.2. Serial Package Methods
For network speed is faster than serial. Module will put serial data in buffer before sending it to network. The data
will be sent to Network as Package. There are 2 ways to end the package and send package to network - Time
Trigger Mode and Length Trigger Mode.
Time Trigger Mode: Default package time is 4 bytes sending interval and use can set between 0~65535.
Length Trigger Mode: Default package length is 1460 and user can set between 0~1460.
2.2.3. Baud Rate Synchronization
When module works with USR devices or software, serial parameter will change dynamically according to
network protocol. Customer can modify serial parameter by sending data conformed to specific protocol via
network. It is temporary, when restart DTU, the parameters back to original parameters.
2.3.Modbus protocol transmission
Work mode: Modbus_RTU_Master, Modbus_ASCII_Master, Modbus_RTU_Slave, Modbus_ASCII_ Slave. Work mode
can be defined according to the serial port device of M511 and Modbus protocol. For example, serial port device is
Modbus Master and Modbus protocol is ASCII protocol, work mode is Modbus_ASCII_Master.
2.3.1.Modbus Master
Modbus Master mode means serial port device connected to M511 is Modbus Master.
1. M511 work in Modbus Master mode allow at most 32 Modbus Masters connect through RS485/RS422 to
achieve RS485/RS422 multiple Masters Polling function. But speed of RS485/RS422 interface will be a little slow
because of the limitation of RS485/RS422 baud rate.
2. When M511 work in Modbus Master mode can query information of different Modbus slaves by sending query
command with ID of specific Modbus slave. M511 allow at most 8 target server.
3. Modbus work in Modbus Master mode can apply to four applications: One Master to one Slave; one Master to
multiple Slaves; multiple Masters to one Slave; multiple Masters to multiple Slaves.
Application diagram as follows:
Figure 12 One Master to one Slave
User can change Modbus Master mode parameters by web server as follow:
