Sutron Corporation X-Link Operations & Maintenance Manual, Rev 1.63 5/24/2016 pg. 169
18.
Modbus
Modbus is a communications protocol commonly used in industrial applications.
Please see the
Wikipedia entry
for more details.
X-Link can be configured as a Modbus slave device. That means that some other
Modbus master can collect data from X-Link.
Generally, Modbus is used to access sensor readings. The reading from every
sensor measurement that is setup on X-Link can be accessed via Modbus.
Additionally, extended Modbus commands allow the downloading of X-Link's
log, reading and writing X-Link's setup, accessing status information, and more.
18.1.
Modbus Hardware Interface
There are two interfaces that support Modbus communication:
o
RS-485
o
Cell modem (GPRSLink, HSPALink, and CDMALink)
Each interface can be setup independently of the other one. Each interface has
its own setup.
Please note that Modbus RS-485 and SDI-12 are mutually exclusive. If Modbus
RS-485 is enabled, X-Link will NOT be able to collect data from SDI-12 sensors.
18.1.1.
Wiring Modbus RS-485
X-Link has a half duplex RS-485 interface. That means that the same lines are
used for sending and recieving data.
Only two lines need to be connected to use RS-485:
RS-485 A
RS-485 B
When wiring, connect the Modbus master's RS-485 A line to X-Link's RS-485 A
Line. Do the same for RS-485 B.
18.1.1.1.
Troubleshooting Modbus RS-485
If the Modbus master is unable to talk to X-Link, there are two potential causes:
