UM3487E Datasheet, PDF (5/14 Pages) Union Semiconductor, Inc. – ±15kV ESD-Protected, Fail-Safe, Hot-Swappable Auto Polarity Reversal RS-485 Transceivers

UM3487E
Non-Polarity Features
The Polarities of driver and receiver is always kept the same status. When DE=/RE=LOGIC 0 and
RO is standing LOGIC 0 for T_S time, the polarities will be reversed automatically.
Parameter
Symbol
Test Conditions
Min Typ Max Unit
Waiting Time for Inverting
T_s
DE=/RE=L, RO keeps L 150 200 250 ms
Pin Description
Pin Number
1
2
3
4
5
6
7
8
Symbol
RO
/RE
DE
DI
GND
L2
L1
V_CC
Function
Receiver Output.
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.
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.
Driver Input.
Ground
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.
Power Supply for RS-485 transceiver
RS-485 Communication Function Table
Table1. Transmitting
INPUTS
/RE
DE
DI
X
H
H/O
X
H
L
L
L/O
X
H
L/O
X
OUTPUTS
A
B
H
L
L
H
Z
Z
Shutdown
Table2. Receiving
/RE
DE
L
X
L
X
L
X
H
H
H
L
INPUTS
V_ID=V_A-V_B
≥-50mV
≤-200mV
Open/Shorted
X
X
OUTPUTS
RO
H
L
H
Z
Shutdown
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.
________________________________________________________________________
http://www.union-ic.com Rev.02 Jan.2014
5/14