ISL41334IRZ datasheet(13/28 Pages) INTERSIL

13 / 28 page

FN6202.3

November 21, 2007

Typical Application

RS-232 to RS-485 Converter

The ISL81334, ISL41334 are ideal for implementing a single

IC 2-wire (Tx Data, Rx Data) protocol converter, because

each port can be programmed for a different protocol.

Figure 8 illustrates the simple connections to create a single

transceiver RS-232 to RS-485 converter. Depending on the

RS-232 data rate, using an RS-422 bus as an RS-232

“extension cord” can extend the transmission distance up to

4000’ (1220m). A similar circuit on the other end of the cable

completes the conversion to/from RS-232.

Detailed Description

Each of the two ISL81334, ISL41334 ports supports dual

protocols: RS-485/422, and RS-232. RS-485 and RS-422 are

differential (balanced) data transmission standards for use in

high speed (up to 20Mbps) networks, or long haul and noisy

environments. The differential signaling, coupled with RS-485’s

requirement for extended common mode range (CMR) of +12V

to -7V make these transceivers extremely tolerant of ground

potential differences, as well as voltages induced in the cable

by external fields. Both of these effects are real concerns when

communicating over the RS-485, RS-422 maximum distance of

4000’ (1220m). It is important to note that the ISL81334,

ISL41334 don’t follow the RS-485 convention whereby the

inverting I/O is labeled “B/Z”, and the noninverting I/O is “A/Y”.

Thus, in the application diagrams below the 1334 A/Y (B/Z)

pins connect to the B/Z (A/Y) pins of the generic RS-485,

RS-422 ICs.

FIGURE 6A. TEST CIRCUIT

FIGURE 6B. MEASUREMENT POINTS

FIGURE 6. RS-232 DRIVER PROPAGATION DELAY AND TRANSITION TIMES

FIGURE 7A. TEST CIRCUIT

FIGURE 7B. MEASUREMENT POINTS

FIGURE 7. RS-232 RECEIVER PROPAGATION DELAY AND TRANSITION TIMES

Test Circuits and Waveforms (Continued)

DY,Z

SIGNAL

GENERATOR

Y, Z

OUT (Y,Z)

1.5V

VO+

VO-

DY,Z

SKEW = |tDPHL - tDPLH|

tDPHL

tDPLH

RXEN (QFN ONLY)

A, B

SIGNAL

GENERATOR

RA, RB

CL = 15pF

RA, RB

tRPHL

1.7V

1.3V

VOH

VOL

0.8V

2.4V

tRPLH

A, B

SKEW = |tRPHL - tRPLH|

VCC

DY1

DZ1

0.1µF

V+

V-

C1+

C1-

C2+

C2-

0.1µF

RA1

RB1

525

+C3

GND

+5V

+ 0.1µF

SEL1

ON/OFF

VCC

NOTE: PINOUT FOR SOIC AND SSOP

DY2 19

DE2 18

VCC

RA2

SEL2

VCC

RS-232 IN

RS-232 OUT

RS-485 IN

RS-485 OUT

FIGURE 8. SINGLE IC RS-232 TO RS-485 CONVERTER

TxD

RxD

ISL81334, ISL41334

ISL41334IRZ Datasheet(PDF) 13 Page - Intersil Corporation

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