Telemetry Module MT-102 User's Manual - BlueNote Communications

packet routing - useful for unambiguous definition of where in transmitted frames the
recipient address is placed and how it is recorded without knowing the foreign protocol.
In that case, routing table can be created to eliminate redundant transmissions.
transmission channel reservation - diminishes transmitted data volume provided that
multiple queries of one device are executed not knowing the foreign protocol. When
channel reservation is employed only the first query is sent to all modules defined in
Authorized IP numbers list. After reception of the response the module reserves, for a
defined time, the direct communication channel with the module that responded to the
last query thus creating a temporary point to point connection. The reservation time is
counted since reception of last GPRS packet. Consecutive packets received from that
module prolong channel reservation while sending packets does not prolong the
reservation.
When channel reservation time is set to 0 [sec], the module does not reserve channel
and works in standard mode receiving and sending packets from all defined remote units.
7.3. Modbus RTU Master mode
In this mode, the module cooperates with the device acting as MODBUS RTU MASTER.
The master sends queries addressed to Slave devices to module's PORT2.
Upon reception of the frame at PORT2, the module verifies recipient device address. Since
module's own resources are available in Modbus RTU Master mode under Modbus ID
assigned to module, the instruction is carried out and replay sent to PORT2 (to the master)
when matched with address.
Frames with other Modbus ID addresses transmitted via GPRS are routed to other recipients
on the basis of a table assigning IP addresses to Modbus IDs (routing table - redirection). In
other words, MT-102 acts as a router of packets sent from Master to remote Slave units. This
mode enables creation of data acquisition system, where standard queries generated by PLC
controller or any other device working in Modbus RTU Master mode. This solution is not
recommended if master role is played by a PC running Windows 2000 or newer and collected
data is used by applications capable of using data collected by OPC or written in CSV or SQL
format.
Following rules apply for Modbus RTU Master mode:
Frames are sent only to recipients having Modbus ID matching address received via
PORT2.
All frames received at PORT2 are sent to recipients having Modbus ID=0 written in the
table.
Frames with address 0 (broadcast frames) are set to all recipients declared in the
routing table.
Repeating IP address in the table does not cause multiple transmission to the same
recipient. This makes sending frames with different Modbus IDs to same IP recipient
possible, connecting a large number of devices with various Modbus IDs to PORT2 of
the remote module operating in MODBUS RTU Slave mode.
The frame will be dispatched to recipient only when IP address is defined in Authorized
numbers list of GPRS section and sending option is checked.
After receiving frame via GPRS, the module checks if it is addressed to its internal
resources (address matches declared Modbus ID). If that is the case, the instruction is
carried out and confirmation sent to sender. This behavior enables creation of Multimaster
systems securing proper data transmission and access to all resources of the
system.
If Modbus ID of received frame does not match module's ID, the frame is forwarded to
PORT2 and may be received by the Master device.
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