Sutron Corporation X-Link Operations & Maintenance Manual, Rev 1.63 5/24/2016 pg. 171
18.2.1.2.
Modbus Cell Protocol
Within Modbus, there are different protocols:
RTU
ASCII
TCP
RTU is the most basic Modbus protocol and is commonly used for directly wired
systems. It requires a robust connection as it has stringent timing requirements.
The ASCII protocol is most forgiving of timing issues and will produce the best
communication results when communicating over a modem. However, the
ASCII protocol also uses the most bandwidth.
The TCP protocol is traditionally used over Ethernet. It takes advantage of the
error checking and correction built into TCP/IP.
Please see the
Wikipedia entry
for more details on the protocols.
18.2.1.3.
Modbus Cell Device ID
The Device ID is only relevant for RTU and ASCII protocols. It is used to allow
multiple Modbus slaves to be connected to one Modbus master.
The device ID is the address that is used by the Modbus master to select which
device to communicate with. Each slave on the bus must have a unique device
ID ranging from 1 – 247. Address ‘0’ is reserved as the broadcast address.
When a Modbus master issues a command, it includes the Device ID in the
command. Only the Modbus slave with a matching ID is allowed to answer. If
multiple slaves have the same ID, communication will not work.
Device ID is sometimes referred to as Slave Address, Station Address, or Slave ID.
18.2.1.4.
Modbus RS485 Enable
To talk Modbus over RS-485,
Modbus RS485 Enable
must be turned on.
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.
18.2.1.5.
Modbus Protocol
Modbus over RS-485 only allows RTU and ASCII protocols. RTU is the default
value. Please see the
Modbus Cell Protocol
above for details on Modbus
protocols.
18.2.1.6.
Modbus RS485 Device ID
Please see the
Modbus Cell Device ID
description.
