Specifications

ManualsBrandsQuatech ManualsTV CableAVD-USB2-500

www.quatech.com

RS-232 and RS-422/485

In order for DCE and DTE devices to communicate with each

other, two wires must be used--one for transmission and the

other for reception--and both devices must not use the same

wire for the same purpose.

Should this happen, nothing

would get communicated

because both devices would

be talking on the same line

and listening to a line on

which nothing is transmitted.

To solve this problem, DTE and

DCE devices have complementary

pinouts to allow terminals and

modems to be connected directly

using a one-to-one cable (see

above-right).

Situations arise in which no DCE device is needed, such as a

desktop computer communicating with a laptop. In this case, a

null modem cable or modem eliminator cable

is used to connect

the two DTE devices. This cable effectively changes the wires

the second device uses for transmission and reception (see above-

left) to assure that both sides can communicate.

Connectors: The Communication Conduit

As discussed in the asynchronous and synchronous

communication sections, there is more to a serial transmission

than simply data. Additional information must be transmitted

between both ends of a conversation to make sure that when

Point A sends, Point B is listening, and vice versa. This is called

handshaking.

These handshaking lines take-up considerable space

on a serial connector.

Connectors for RS-232 devices are always constructed using

standard assignments for the wires in a RS-232 cable in order to

maintain the DTE-DCE relationship described above. These

connectors can be modular (phone jack) or male D-shell (pins

configured in a rough "D" shape which fit into sockets on the

device). The signal assignments for the RS-232 wires follow.

The descriptions reference the standard D-9 and D-25 connectors

used by most serial devices, however the definitions are applicable

to modular connectors as well (though in modular connections

not all of the handshaking signals are implemented). Pages 62,

70-73 and 78 detail Quatech modular adapters for PCI,

CompactPCI, and ISA, and include modular connector pinout

information.

RS-232 Signal Descriptions

Abbreviations used in the following definitions of RS-232 wire

functions will be used throughout the catalog.

DTR:

Data Terminal Ready

--Used by a DTE to signal that it is

plugged in and available to begin communication.

DSR:

Data Set Ready

--Sister signal to DTR, it is used by the DCE

to indicate it is ready to begin communication.

CTS:

Clear to Send

--Used by DCE to signal it is available to send

data, and also used in response to an RTS request for data.

RTS:

Request to Send

--Used by a DTE to indicate that it wants

to send data. Also, in a multi-drop network, used to turn carrier

on the modem on and off.

DCD:

Data Carrier Detect

--Used by a DCE to indicate to the DTE

that it has received a carrier signal from the modem and that real

data is being transmitted.

RI:

Ring Indicator

--Used by a DCE modem to tell the DTE that

the phone is ringing and that data will be forthcoming.

TxD:

Transmit Data

--This wire is used for sending data.

RxD:

Receive Data

--This line is used for receiving data.

GND:

Signal Ground

--This pin is the same for DTE and DCE

devices, and it provides the return path for both data and

handshake signals.

Synchronous Communication Only

TxCLK:

Transmit Signal Element Timing

--Used by DTE to provide

DCE with timing information for data transfer.

RxCLK:

Receiver Signal Element Timing

--Used by DCE to provide

DTE with timing information for data transfer.

LLBK:

Local Loopback

--Used by DTE to make sure the local

transmit and receive interface is functioning properly.

RLBK:

Remote Loopback

--Used by DTE to make sure a remote

transmit/receive interface is functioning properly.

TEST MODE:

Test Mode

--Used by DCE to indicate that it is testing

itself in response to a local or remote loopback signal from a DTE.

(RS-232 Serial Connectors)

Modular

all pins used

20 22

15 16

18 19

D-9

all pins used

D-25: Black pins always used

Green pins for synchronous only

White for asynchronous only

23456

GND