NOVUS AirGate-GPRS - Manual (Page 23)

AirGate-GPRS
NOVUS AUTOMATION 23/29
RS485 - 1
The RS485 interface of the AirGate-GPRS is located in terminals 1, 2, and 3 and behaves as a Modbus RTU master,
allowing data from other devices on the bus to be read by AirGate-GPRS either directly (remote channels) or by other
masters using the AirGate-GPRS (gateway). Please read the section “Remote Channels” for further details regarding
the implementation of a Modbus RTU network with the AirGate-GPRS in the role of master.
Modbus commands received by AirGate-GPRS where the destination address is the AirGate itself will be answered
by the AirGate-GPRS. All of the Modbus commands received by AirGate-GPRS where the destination address is not
of the AirGate-GPRS itself will be forwarded to the Modbus RTU network, because it is understood that the
command is addressed to the slave of this network. More details in the chapter “Data and Routing Communication”.
The RS485 - 1 interface can be configured to operate at the following velocities (baud rates): 1200, 2400, 4800, 9600,
19200, 38400, 57600 and 115200. Also, it can be configured to operate with one or two stop bits, and even, odd, or no
parities.
Further details regarding the implementation of a network of Modbus devices via RS485 can be found in the document
“Basic Concepts of RS485 and RS482” available with the CD that comes with the product.
D1 D D+ B Two way data line. Terminal 1
D0 D D- A Inverted two way data line. Terminal 2
C
Optional connection that improves the communication
performance.
Terminal 3
GND
RS485 - 2
Interface RS485-2 of AirGate-GPRS is located in terminals 4, 5, and 6 and can be enabled or disabled. When disabled,
it offers no consistency regarding the traffic that may exist on the data bus. When enabled, it can be configured to
operate as a Modbus RTU slave or a master.
Slave
When operating as a Modbus RTU slave, the equipment provides the values of the channels to be accessed by the
Modbus network master, either a CLP, a type of supervisory software, or some other device. Also, it allows for the
accessing of slaves that are connected to RS485-1 using the routing (see chapter “Data Communication and
Routing").
Master
When operating as a Modbus RTU master, it allows data from other devices on the bus be read by AirGate-GPRS
and used by it in the records, alarms, the virtual channels, or simply available from another interface (such as
Ethernet). Please see the section “Remote Channels” for more details as to how to implement a Modbus RTU
network with AirGate-GPRS in the role of master.
Modbus commands received by AirGate-GPRS, with a destination address from the AirGate itself, will be answered
by the AirGate-GPRS. All of the Modbus commands received by AirGate-GPRS with a destination address other
than the AirGate will be forwarded to the Modbus RT network, because it is understood that the command is
addressed to a slave of that network. More details are available in the section “Data Communication and Routing”.
The RS485-2 interface can be configured to operate at the following speeds (baud rates): 1200, 2400, 4800, 9600,
19200, 38400, 57600 and 115200. Also, it can be configured to operate with one or two stop bits, and even, odd, or no
parities.
Further details about the implementation of a network of Modbus devices via RS485 can be found in the document
“Basic Concepts of RS485 and RS422” available on the CD that comes with the product.
D1 D D+ B Bidirectional data line. Terminal 4
D0 D D- A Bidirectional inverted data line. Terminal 5
C
Optional connection that improves the communication
performance.
Terminal 6
GND
REMOTE CHANNELS
The AirGate-GPRS can operate as an autonomous master for a Modbus RTU network (see configuration of interfaces
RS485), as can read up to 10 registers of other devices (Modbus slaves) and use these registers in alarms. Each one of
these registers read from other slaves are called “remote channels”.
The equipment begins the reading of the channels in the order they were created at the time of configuration. This way, it
continues reading all the channels, respecting the time between commands, until it has read them all. After the sweeping
interval, it restarts the reading of all of the remote channels. If the reading of the channels takes longer that the
configured sweeping interval, it immediately restarts the reading of the channels.
If the slave takes longer that the configured response time, it will be considered a communication error. Likewise,
response packets with invalid CRCs or time between bytes larger than what is specified by the standard will be
considered errors. If there is a communication error in the reading of the remote channel, it tries again until the number of
configured attempts has been reached. If the error persists, the configured error value for the channel will be assumed.