Date: 8/3/04

+ 5V Powered Multi-Channel RS-232 Drivers/Receivers

© Copyright 2004 Sipex Corporation

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cate. Once the computer is powered–up and ready,

it will send out a signal on the DTR to inform the

printer that it is powered–up and ready to go. The

printer really doesn’t care, since it will simply print

data as it is received. Accordingly, this pin is not

needed at the printer.

Data Set Ready (DSR)

Peripheral devices use this line to tell the computer

that they are on–line and ready to communicate.

When the printer is turned on and has completed its

self–test routine (assuming it does one), it will send

a signal to the PC by asserting this line.

Request To Send (RTS)

The computer activates this line to notify the

peripheral device that it is ready to send data. In this

example, the computer notifies the printer that it is

ready to send data to be printed by the printer.

Clear To Send (CTS)

This is the line on which the peripheral device tells

the computer that it is ready to receive data from

the computer. If the printer was not ready, i.e. it

was out of paper, for example, it would not assert

this line. Once the printer was ready to receive data

from the PC, it would assert this line. When it

receives the CTS signal from the printer, the PC

knows that a data transmission path has been

established between itself and the printer.

Transmitted Data (TD or TX)

This is the pin on which the computer sends the

actual data signal representing the actual informa-

tion to be printed, i.e. a positive voltage (+3V to

+15V) to represent a logic “0”, and a negative

voltage (-3V to -15V) to represent a logic “1”.

Ring Indicator (RI)

This line is used by the peripheral device to tell the

computer that a remote device wants to start com-

municating. A modem would activate the RI line

to tell the computer that a remote modem was

calling, i.e. the phone is ringing. In the case of a

printer, this line is unused.

Data Carrier Detect (DCD)

This line is used by a peripheral device to tell the

computer to expect to start receiving data at any

time. Since the printer would not be sending data

to the PC in this case this line is not needed.

Received Data (RD or RX)

This is the pin on which the computer receives the

incoming data signal, i.e. a positive voltage (+3V

to +15V) to represent a logic “0”, and a negative

voltage (-3V to -15V) to represent a logic “1”.

Again, in this instance, since the printer will not be

sending the PC any data, this line is not needed.