isl8485e Intersil Corporation, isl8485e Datasheet - Page 8

• Manufacturer Part Number: isl8485e
• Description: 5v, Half Duplex, 5mbps, ?15kv Esd Protected, Rs-485/rs-422 Transceiver
• Manufacturer: Intersil Corporation

Test Circuits and Waveforms
Application Information
RS-485 and RS-422 are differential (balanced) data
transmission standards for use in long haul or noisy
environments. RS-422 is a subset of RS-485, so RS-485
transceivers are also RS-422 compliant. RS-422 is a point-
to-multipoint (multidrop) standard, which allows only one
driver and up to 10 (assuming one unit load devices)
receivers on each bus. RS-485 is a true multipoint standard,
which allows up to 32 one unit load devices (any
combination of drivers and receivers) on each bus. To allow
for multipoint operation, the RS-485 spec requires that
drivers must handle bus contention without sustaining any
damage.
Another important advantage of RS-485 is the extended
common mode range (CMR), which specifies that the driver
outputs and receiver inputs withstand signals that range from
+12V to -7V. RS-422 and RS-485 are intended for runs as
long as 4000’, so the wide CMR is necessary to handle
(SHDN) FOR ISL8483E ONLY
SIGNAL
GENERATOR
t
t
ZH(SHDN)
ZL(SHDN)
PARAMETER
t
t
ZH
ZL
(Note 6)
(Note 6)
t
t
HZ
LZ
SIGNAL
GENERATOR
(Note 9)
(Note 9)
+1.5V
FIGURE 4A. TEST CIRCUIT
FIGURE 5A. TEST CIRCUIT
RE
A
B
B
A
RE
DE
0
0
0
0
0
0
R
8
R
RO
RO
+1.5V
+1.5V
+1.5V
-1.5V
-1.5V
-1.5V
A
FIGURE 5. RECEIVER ENABLE AND DISABLE TIMES
(Continued)
15pF
FIGURE 4. RECEIVER PROPAGATION DELAY
1kΩ
15pF
SW
ISL8483E, ISL8485E
GND
GND
GND
V
V
V
SW
CC
CC
CC
GND
V
CC
ground potential differences, as well as voltages induced in
the cable by external fields.
Receiver Features
These devices utilize a differential input receiver for maximum
noise immunity and common mode rejection. Input sensitivity
is ±200mV, as required by the RS422 and RS-485
specifications.
Receiver input impedance surpasses the RS-422 spec of
4kΩ, and meets the RS-485 “Unit Load” requirement of 12kΩ
minimum.
Receiver inputs function with common mode voltages as
great as ±7V outside the power supplies (i.e., +12V and
-7V), making them ideal for long networks where induced
voltages are a realistic concern.
All the receivers include a “fail-safe if open” function that
guarantees a high level receiver output if the receiver inputs
are unconnected (floating).
t
t
ZH
ZL
RO
A
NOTE 7
RE
RO
NOTE 7
RO
, t
, t
ZH(SHDN)
ZL(SHDN)
NOTE 7
FIGURE 4B. MEASUREMENT POINTS
FIGURE 5B. MEASUREMENT POINTS
t
PLH
1.5V
1.5V
OUTPUT HIGH
50%
1.5V
1.5V
OUTPUT LOW
t
PHL
1.5V
t
t
HZ
1.5V
LZ
50%
V
V
OH
OL
- 0.5V
+ 0.5V
3V
0V
3V
0V
V
0V
V
V
V
CC
0V
OH
OL
CC