Product manual

B Protocols TAC Xenta Server – Gateway, Technical Manual
118 (184) Schneider Electric Buildings AB, June 2011
04-00124-06-en
B.1.1 Modbus Master Networks
A Modbus Master Network consists of a single master and one or more
independent slaves interconnected by an RS-485 serial link. While the
Xenta 913 is attached to the network it continuously polls the attached
slaves to read the required register values. It can also write the necessary
control system values out to the slaves. All devices on the network must
use the same Modbus framing mode (RTU or ASCII).
Each slave device must have a unique numeric address on the network.
Slave addresses can be in the range 1 to 247 (address 0 is reserved for
broadcasts so is not normally applicable to a single device). However,
not all 247 addresses can be used since a maximum of 32 slave devices
can be physically connected to a Modbus serial line. If more than 32
slaves are required one or more RS-485 Network extenders can be fit-
ted.
Some Modbus routers can represent multiple slave devices on a sub-net-
work. In this case, the connection to the router can be RS-232 but the
Xenta 913 will still be able to address the slave devices as if they were
directly connected to it. Some routers use a device address of 0 to access
values within the router itself rather than the slave devices on its
sub-network.
Note
• Regardless of the Modbus network configuration, all connected
slave devices must be assigned a unique numeric address.