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http://www.union-ic.com Rev.02 Jan.2014

5/14

UM3487E

Non-Polarity Features

The Polarities of driver and receiver is always kept the same status. When DE=/RE=LOGIC 0 and

Parameter

Symbol

Test Conditions

Min

Typ

Max

Unit

Waiting Time for Inverting

DE=/RE=L, RO keeps L

150

200

250

ms

Pin Description

Pin Number

Symbol

Function

1

RO

Receiver Output.

2

/RE

Receiver Enable. Drive /RE low to enable Receiver, RO is high

impedance when /RE is high. Drive /RE high and DE low to enter

low-power shutdown mode.

3

DE

Driver Enable. Drive DE high to enable drivers. The outputs are

high impedance when DE is low. Drive /RE high and DE low to

enter low-power shutdown mode.

4

DI

Driver Input.

5

GND

Ground

6

L2

Auto Polarity Reversal Receiver Input and Driver Output Pin.

When power up, the bus pins have their normal polarity

definition of L2 as non inverting and L1 as inverting; otherwise

L2 become inverting and L1 become non inverting for reversal

status.

7

L1

8

Power Supply for RS-485 transceiver

RS-485 Communication Function Table

Table1. Transmitting

INPUTS

OUTPUTS

/RE

DE

DI

A

B

X

H

H/O

H

L

X

H

L

L

H

L

L/O

X

Z

Z

H

L/O

X

Shutdown

Table2. Receiving

H: High, L: Low, X: Do not care, Z: High impedance.

In normal RS485 Polarity Status, L2=A and L1=B, otherwise L2=B and L1=A.

INPUTS

OUTPUTS

/RE

DE

RO

L

X

≥-50mV

H

L

X

≤-200mV

L

L

X

Open/Shorted

H

H

H

X

Z

H

L

X

Shutdown