28
•
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 behaviour enables creation of Multi-
master 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.
7.4. Modbus RTU Slave mode
In this mode, the module acts as a network node serving both own resources and all
connected to PORT2 devices operating in Modbus RTU Slave mode, waiting for GPRS data
frames.
Upon reception of the frame, it investigates recipient's address (matching declared Modbus
ID with its own).
If the address matches, the instruction is carried out and confirmation set to sender. If it
does not match the frame is forwarded to PORT2. The module waits for 0,5 sec for reply.
When reply comes or the time elapses, the module whether new data frame arrived via
GPRS.
Sending frames not addressed to module's ID to PORT2 is unconditional as module does
not have the list of connected to PORT2 Slave devices.
Replies are sent to sender as standard. Sending of replies to additional Master units can be
defined in routing table.
The IP address of additional Master is stated in the second column of the table, and the
device Modbus ID from which replies have to be sent to additional master are stated in
third column.
If third column states "0", replies from all slaves will be sent to corresponding IP address.
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