User manual

IEC61131 User and Reference Manual
April 22, 2008
375
TeleBUS Protocols Overview
The TeleBUS communication protocols provide a standard communication interface to
SCADAPack and TeleSAFE controllers. The TeleBUS protocols are compatible with the
widely used Modbus RTU and ASCII protocols. Additional TeleBUS commands provide
remote programming and diagnostics capability.
The TeleBUS protocols operate on a wide variety of serial data links. These include RS-232
serial ports, RS-485 serial ports, radios, leased line modems, and dial up modems. The
protocols are generally independent of the communication parameters of the link, with a few
exceptions.
TeleBUS protocol commands may be directed to a specific device, identified by its station
number, or broadcast to all devices. Using extended addressing up to 65534 devices may
connect to one communication network.
The TeleBUS protocols provide full access to the I/O database in the controller. The I/O
database contains user-assigned registers and general purpose registers. Assigned
registers map directly to the I/O hardware or system parameter in the controller. General
purpose registers can be used by ladder logic and C application programs to store
processed information, and to receive information from a remote device.
Application programs can initiate communication with remote devices. A multiple port
controller can be a data concentrator for remote devices, by polling remote devices on one
port and responding as a slave on another port.
The protocol type, communication parameters and station address are configured separately
for each serial port on a controller. One controller can appear as different stations on
different communication networks. The port configuration can be set from an application
program, from the TelePACE programming software, or from another Modbus compatible
device.
Compatibility
There are two TeleBUS protocols. The TeleBUS RTU protocol is compatible with the
Modbus RTU protocol. The TeleBUS ASCII protocol is compatible with the Modbus ASCII
protocol.
Compatibility refers to communication only. The protocol defines communication aspects
such as commands, syntax, message framing, error handling and addressing. The
controllers do not mimic the internal functioning of any programmable controller. Device
specific functions – those that relate to the hardware or programming of a specific
programmable controller – are not implemented.
Serial Port Configuration
Communication Parameters
The TeleBUS protocols are, in general, independent of the serial communication
parameters. The baud rate, word length and parity may be chosen to suit the host computer
and the characteristics of the data link.
The port configuration can be set in four ways:
 using the TelePACE program;
 using the set_port function from a C application program;