Communication Protocols; Pc Communication; Modbus Tcp And Modbus Rtu - Allen-Bradley Rockwell Automation 857 User Manual

7-6
Communications

Communication Protocols

857-UM001A-EN-P – July 2009
These protocols enable the transfer of the following type of data:
•
events
•
status information
•
measurements
•
control commands
•
clock synchronizing
•
Settings (SPA-bus and embedded SPA-bus only)

PC Communication

PC communication is using an Allen-Bradley specified command
line interface. The SetPointPS program can communicate using the
local RS-232 port or using TCP/IP and ethernet interface. It is also
possible to select SPA-bus protocol for the local port and configure
the SetPointPS to embed the command line interface inside SPA-bus
messages. For TCP/IP configuration see "TCP/IP".

Modbus TCP and Modbus RTU

These Modbus protocols are often used in power plants and in
industrial applications. The difference between these two protocols is
the media. Modbus TCP uses Ethernet and Modbus RTU uses
asynchronous communication (RS-485, optic fibre, RS-232).
SetPointPS will show the list of all available data items for Modbus.
The Modbus communication is activated usually for remote port via
a menu selection with parameter "Protocol". See "Communication
Ports".
For TCP/IP configuration, see "TCP/IP".
Table 7.5 – Modbus TCP and Modbus RTU Parameters
Parameter Value
Addr 1 – 247
bit/s 1200
2400
4800
9600
19200
Parity None
Even
Odd
Set = An editable parameter (password needed)
Unit Description
Modbus address for the device.
Broadcast address 0 can be used for
clock synchronizing. Modbus TCP
uses also the TCP port settings.
bps Communication speed for Modbus
RTU
Parity for Modbus RTU
Note
Set
Set
Set