Rockwell Automation 1747-L5xx SLC 500 Modular Hardware Style User Manual - Manual (Page 210)

Publication 1747-UM011G-EN-P - June 2008
210 RS-232 Communication Interface
Modbus RTU Master
Communication Modbus RTU communication lets you connect the SLC 5/03, SLC 5/04, and
SLC 5/05 processors to Modbus RTU slave devices for exchange of data
values.
For an overview of the Modbus RTU Master protocol modem, refer to the
SLC 500 Instruction Set Reference Manual (1747-RM001).
ASCII Communication ASCII protocol lets you connect the SLC 5/03, SLC 5/04, and SLC 5/05
processors to serial printers, personal computers, and other third-party
devices. ASCII protocol lets your ladder program manage ASCII data.
DF1/Modbus RTU
Communication Protocol
Modems Overview You can connect the SLC 5/03, SLC 5/04, and SLC 5/05 processors to
several types of modems. In all cases, the processors act as Data Terminal
Equipment (DTE). DTE send and/or receive data on a network. Modem or
line drivers act as Data Communication Equipment (DCE), which provide the
signal conversion and coding required for communication between DTE and
data circuits. Other DCE include phone-line modems and specialized
modems, such as radio and satellite-link modems.
In addition to Common Return (COM), Receive Data (RXD), and Transmit
Data (TXD), the following active modem-control lines are provided on the
SLC 5/03, SLC 5/04, and SLC 5/05 processors.
RTS (Request to Send) - this output signal indicates to the modem or other
DCE that the DTE wants to transmit.
CTS (Clear to Send) - this input signal from the modem indicates the modem
is ready to receive the transmission by the DTE for forwarding over a link.
DSR (Data Set Ready) - this input signal indicates the DCE device is ready for
operation. Loss of this signal causes a modem-lost condition in the processor.
DTR (Data Terminal Ready) - this output signal from the DTE indicates that
it is ready for operation. You can also use this signal with the processor to
initiate DTR dialing in dial-up modems that support such a feature.
Modular Controller with
SLC 5/03 Processor
RS-232 Channel 0
1747-CP3 Cable