NOVUS AirGate-GPRS - Manual (Page 26)

AirGate-GPRS
NOVUS AUTOMATION 26/29
• USB device, acting as a slave in the Modbus RTU protocol.
• GPRS, acting as a server (slave) with the Modbus TCP protocols or the Modbus over TCP (configurable).
All of the equipment configuration, as well as the reading of the input data, is done via Modbus protocol.
In the chapter “Modbus Commands and Tables of Registers” you can find the necessary information to do the reading to
the data of the input channels without using the Configuration software. To ensure the correct configuration and the data
collection of AirGate-GPRS, always use the recommended software. After configuring the equipment, the data of the
inputs or the slaves connected to it can be accessed by any other software with the Modbus communication capacity.
ROUTING
The AirGate-GPRS has the capacity to rotate commends between its interfaces. Upon receiving a Modbus command
from any of its interfaces (USB, GPRS or RS485 slave), it checks if the address of the destination is its own address. If it
is, is processes the command and responds to the master itself. If it is not, it assumes that the command is destined for
another slave that is connected to some of its RS485 interfaces and forwards the command to it.
All of the Modbus broadcast commands will be routed to the RS485 interfaces. In other words, the
AirGate-GPRS does not accept broadcast commands sent to it self.
ONE RS485 MASTER INTERFACE
If we use only the RS485 – 1 interface configured and a Modbus master, all of the commands coming from different
slave interfaces (USB, GPRS, and/or RS485 - 2) that are not destined for the AirGate-GPRS will be routed to this
interface.
If you receive Modbus requests from different interfaces at the same time, it will route the first to be received to the
RS485 - 1 slave, making the others wait. As soon as it receives an answer from the slave, it will be routed back to the
requesting interface (master) and the next in line will be sent to RS485 -1.
TWO RS485 MASTER INTERFACES
If we have the two RS485 interfaces configured with the Modbus master, all of the commands coming from the different
slave interfaces (USB and/or GPRS) that are not sent to the AirGate-GPRS will be routed to these interfaces.
The first time you receive a command sent to a specific slave (other than itself), it will send this command two both
RS485 interfaces, because it still does not know in which the destination slave is located. Upon receiving an answer from
the slave, the AirGate-GPRS “learns” where it is. Upon receiving the next command for this slave, it will forward the
command only to that RS485 interface, reducing the traffic on the other bus.
If Modbus requests are received from several interfaces at the same time, it will route the first to be received by the
RS485 -1 slave, leaving the others waiting. As soon as it receives an answer from the slave, it will be routed back to the
requesting interface (the master) and the next in line will be forwarded to RS485 – 1.