AD7306

–8–

REV. D

Single-Ended Data Transmission

Single-ended interfaces are used for low speed, short distance

communications such as from a computer terminal to a printer.

A single line is used to carry the signal. Various standards have

been developed to standardize the communication link, the most

popular of these being the RS-232. The RS-232 standard was

introduced in 1962 by the EIA and has been widely used

throughout the industry. The standard has been revised several

times, and the current revision is known as EIA-232E. The

RS-232 standard is suitable for single-ended data transmission

at relatively slow data rates over short distances. A typical

RS-232 interface is shown in Figure 14.

RS-232 CHANNEL

DATA

IN

DATA

OUT

RX

TX

Figure 14. Single-Ended RS-232 Interface

Differential Data Transmission

When transmitting at high data rates, over long distances and

through noisy environments, single-ended data transmission is

often inadequate. In this type of application, differential data

transmission offers superior performance. Differential transmis-

sion uses two signal lines to transmit data. It rejects ground

shifts and is insensitive to noise signals which appear as com-

mon mode voltages on the transmission lines. To accommodate

faster data communication, the differential RS-422 standard was

developed. Therefore, it can be used to reliably transmit data at

higher speeds and over longer distances than single-ended trans-

mission. A typical RS-422 interface is shown in Figure 15.

RS-422 CHANNEL

DATA

IN

DATA

OUT

RX

TX

Figure 15. Differential RS-422 Interface

Table I. Comparison of RS-232 and RS-422 Interface Standards

Specification

EIA-232E

RS-422

Transmission Type

Single-Ended

Differential

Maximum Data Rate

20 kB/s

10 MB/s

Maximum Cable Length

Load Dependent

4000 ft.

Minimum Driver Output Voltage

±5 V

±1.5 V

Slew Rate

30 V/

µs max

Receiver Input Resistance

3 k

Ω to 7 kΩ

4 k

Ω min

Receiver Input Sensitivity

±3 V

±200 mV

Receiver Input Voltage Range

±15 V

±7 V

No. of Drivers per Line

1

1

No. of Receivers per Line

1

10