Rs-232 Signal Designations; Dte And Dce - B&B Electronics MIport 3PCIOU1 User Manual

RS-232 Connections/Operation

RS-232 Signal Designations

The primary RS-232 signals are
with GND (ground), they often are referred to as a "3-wire" interface.
The (Request to Send) and
RTS
lines used to indicate to the other device that data can be sent or received.
These lines may be enabled or disabled on a byte-by-byte basis and are used
to prevent buffer overrun or the loss of data.
Two secondary handshaking signals are
(Data Set Ready). They are usually enabled when the device is powered
DSR
up and the port is open. They may be used for flow control by some devices
instead of RTS and CTS.
(Data Carrier Detect) is used by a modem to indicate Carrier to the
DCD
computer so data can be sent/received.
(Ring Indicator) is output by a modem to indicate that the phone or FAX
RI
line has a incoming call, so it can be handled.

DTE and DCE

There are two types of RS-232 ports:
•
(Data Terminal Equipment) which is typically a computer
DTE
•
(Data Communications Equipment) which is typically a modem.
DCE
Data Terminal Equipment (DTE)
When a DTE is connected to a DCE they are linked directly together using a
modem cable wired pin to pin so that the inputs match the outputs of the
other.
Data Communications Equipment (DCE)
When two pieces of equipment of the same type are interconnected (a DTE
connected to a DTE, or a DCE to a DCE), a crossover (often called a null
modem) cable is needed to route the outputs of one to the inputs of the other.
This type of cable is needed to interconnect two computers with RS-232.
Note: Refer to Appendix B for straight-through and null modem cable
diagrams and pinouts.
Chapter 7
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(transmit) and (receive). Together
TD RD
(Clear to Send) signals are handshaking
CTS
(Data Terminal Ready) and
DTR
Manual Documentation Number 3PCIoUx-1008