Rockwell Automation 1747-L5xx SLC 500 Modular Hardware Style User Manual - Manual (Page 274)

Publication 1747-UM011G-EN-P - June 2008
274 Glossary
direct connect
Type of modem that is connected to a dedicated, leased phone line
and is active at all times.
DH +
Data Highway Plus implements peer-to-peer communication with a
token-passing scheme to rotate link mastership among the nodes
connected to that link. Data Highway Plus has the capability for
online programming and is optimized for networks with fewer nodes
(Data Highway Plus supports up to 64 nodes).
DH-485 network
The DH-485 network is a collection of devices connected to the
communication cable allowing information exchange. A
communication network based on the EIA Standard for RS-485 using
an Allen-Bradley proprietary protocol.
discrete input and output (DIO)
The discrete input and output is the transfer of one to 32 words
between a SLC 500 processor and a scanner. All 32 words of input
data and all 32 words of output data are updated on each SLC
program scan.
download
The transfer of program or data files to a device.
DTE
Data Terminal Equipment.
DTE controlled answer
Type of modem that is unattended and is attached directly to the
phone lines. The interface module or the SLC 5/03 processor acts as
the Data Terminal Equipment (DTE) which controls the modem via
the DTR and RTS signals. The module incorporates timeouts and tests
to properly operate these types of modems.
DTR dialing (SLC 5/03 only)
Type of modem that lets you dial a number or end a call based on the
status of the RS232 DTR (Data Terminal Ready) signal. To program the
modem initialization string and phone number into the internal
memory of the modem, use a dumb terminal (or personal computer
running terminal emulation software like Procomm, Window’s