Page 1
Full-Duplex, Low Power,
a
FEATURES
Meets EIA RS-485 Standard
250 kbps Data Rate
Single +5 V 6 10% Supply
–7 V to +12 V Bus Common-Mode Range
12 kV Input Impedance
2 kV EFT Protection Meets IEC1000-4-4
High EM Immunity Meets IEC1000-4-3
Reduced Slew Rate for Low EM Interference
Short Circuit Protection
Excellent Noise Immunity
30 mA Supply Current
APPLICATIONS
Low Power RS-485 Systems
DTE-DCE Interface
Packet Switching
Local Area Networks
Data Concentration
Data Multiplexers
Integrated Services Digital Network (ISDN)
Slew Rate Limited, EIA RS-485 Transceivers
ADM488/ADM489
FUNCTIONAL BLOCK DIAGRAMS
ADM488
RO
RO
RE
DE
R
DI
DI
D
ADM489
R
D
A
B
Z
Y
A
B
Z
Y
GENERAL DESCRIPTION
The ADM488 and ADM489 are low power differential line
transceiver suitable for communication on multipoint bus transmission lines.
They are intended for balanced data transmission and comply
with both EIA Standards RS-485 and RS-422. Both products
contains a single differential line driver and a single differential
line receiver making them suitable for full duplex data transfer.
The ADM489 contains an additional receiver and driver enable
control.
The input impedance is 12 kΩ, allowing 32 transceivers to be
connected on the bus.
The ADM488/ADM489 operates from a single +5 V ± 10%
power supply. Excessive power dissipation caused by bus contention or by output shorting is prevented by a thermal shutdown circuit. This feature forces the driver output into a high
impedance state if during fault conditions a significant temperature increase is detected in the internal driver circuitry.
The receiver contains a fail-safe feature that results in a logic
high output state if the inputs are unconnected (floating).
The ADM488/ADM489 is fabricated on BiCMOS, an advanced mixed technology process combining low power CMOS
with fast switching bipolar technology.
The ADM488/ADM489 is fully specified over the industrial
temperature range and is available in DIP, SOIC and TSSOP
packages.
REV. 0
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 617/329-4700 World Wide Web Site: http://www.analog.com
Fax: 617/326-8703 © Analog Devices, Inc., 1997
Page 2
ADM488/ADM489–SPECIFICA TIONS
(VCC = +5 V 6 10%. All specifications T
otherwise noted)
MIN
to T
MAX
unless
Parameter Min Typ Max Units Test Conditions/Comments
DRIVER
Differential Output Voltage, V
OD
2.0 5.0 V V
5.0 V R = ∞, Figure 1
= 5 V, R = 50 Ω (RS-422), Figure 1
CC
1.5 5.0 V R = 27 Ω (RS-485), Figure 1
1.5 5.0 V V
∆|V
| for Complementary Output States 0.2 V R = 27 Ω or 50 Ω, Figure 1
OD
Common-Mode Output Voltage V
| for Complementary Output States 0.2 V R = 27 Ω or 50 Ω
∆|V
OC
Output Short Circuit Current (V
Output Short Circuit Current (V
CMOS Input Logic Threshold Low, V
CMOS Input Logic Threshold High, V
OC
= High) 250 mA –7 V ≤ VO ≤ +12 V
OUT
= Low) 250 mA –7 V ≤ VO ≤ +12 V
OUT
INL
INH
2.0 1.4 V
3 V R = 27 Ω or 50 Ω, Figure 1
1.4 0.8 V
= –7 V to +12 V, Figure 2, VCC = 5 V ± 5%
TST
Logic Input Current (DE, DI) ±1.0 µA
RECEIVER
Differential Input Threshold Voltage, V
Input Voltage Hysteresis, ∆V
TH
TH
Input Resistance 12 kΩ –7 V ≤ V
Input Current (A, B) +1 mA V
–0.2 +0.2 V –7 V ≤ VCM ≤ +12 V
70 mV VCM = 0 V
≤ +12 V
CM
= 12 V
IN
–0.8 mA V
= –7 V
IN
Logic Enable Input Current (RE) ±1 µA
CMOS Output Voltage Low, V
CMOS Output Voltage High, V
OL
OH
4.0 V I
Short Circuit Output Current 7 85 mA V
Three-State Output Leakage Current ±1.0 µA 0.4 V ≤ V
0.4 V I
= +4.0 mA
OUT
= –4.0 mA
OUT
= GND or V
OUT
≤ +2.4 V
OUT
CC
POWER SUPPLY CURRENT Outputs Unloaded, Receivers Enabled
I
CC
30 60 µA DE = 0 V (Disabled)
37 74 µA DE = 5 V (Enabled)
Specifications subject to change without notice.
TIMING SPECIFICATIONS
(VCC = +5 V 6 10%. All specifications T
MIN
to T
unless otherwise noted)
MAX
Parameter Min Typ Max Units Test Conditions/Comments
DRIVER
Propagation Delay Input to Output T
Driver O/P to O/P T
Driver Rise/Fall Time T
SKEW
R
, T
F
PLH
, T
Driver Enable to Output Valid 250 2000 ns R
Driver Disable Timing 300 3000 ns R
250 2000 ns RL Diff = 54 Ω, CL1 = CL2 = 100 pF, Figure 5
PHL
100 800 ns RL Diff = 54 Ω, CL1 = CL2 = 100 pF, Figure 5
250 2000 ns RL Diff = 54 Ω, CL1 = CL2 = 100 pF, Figure 5
= 500 Ω, CL = 100 pF, Figure 2
L
= 500 Ω, CL = 15 pF, Figure 2
L
Data Rate 250 kbps
RECEIVER
Propagation Delay Input to Output T
Skew |T
PLH–TPHL
Receiver Enable T
Receiver Disable T
| 100 ns
EN1
EN2
PLH
, T
250 2000 ns CL = 15 pF, Figure 5
PHL
10 50 ns RL = 1 kΩ, CL = 15 pF, Figure 4
10 50 ns RL = 1 kΩ, CL = 15 pF, Figure 4
Data Rate 250 kbps
Specifications subject to change without notice.
–2–
REV. 0
Page 3
ADM488/ADM489
ABSOLUTE MAXIMUM RATINGS*
(TA = +25°C unless otherwise noted)
VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +7 V
Inputs
Driver Input (DI) . . . . . . . . . . . . . . . –0.3 V to V
Control Inputs (DE, RE) . . . . . . . . . –0.3 V to V
+ 0.3 V
CC
+ 0.3 V
CC
Receiver Inputs (A, B) . . . . . . . . . . . . . . . . –14 V to +14 V
Outputs
Driver Outputs . . . . . . . . . . . . . . . . . . . . . –14 V to +12.5 V
Receiver Output . . . . . . . . . . . . . . . . –0.5 V to V
+ 0.5 V
CC
Power Dissipation 8-Lead DIP . . . . . . . . . . . . . . . . . 700 mW
θ
, Thermal Impedance . . . . . . . . . . . . . . . . . . . 120°C/W
JA
Power Dissipation 8-Lead SOIC . . . . . . . . . . . . . . . . 520 mW
θ
, Thermal Impedance . . . . . . . . . . . . . . . . . . . 110°C/W
JA
Power Dissipation 14-Lead DIP . . . . . . . . . . . . . . . . 800 mW
θ
, Thermal Impedance . . . . . . . . . . . . . . . . . . . 140°C/W
JA
Power Dissipation 16-Lead TSSOP . . . . . . . . . . . . . . 800 mW
θ
, Thermal Impedance . . . . . . . . . . . . . . . . . . . 150°C/W
JA
Operating Temperature Range
Industrial (A Version) . . . . . . . . . . . . . . . –40°C to +85°C
Storage Temperature Range . . . . . . . . . . . . –65°C to +150°C
Lead Temperature (Soldering, 10 secs) . . . . . . . . . . . +300°C
Vapor Phase (60 secs) . . . . . . . . . . . . . . . . . . . . . . +215°C
Infrared (15 secs) . . . . . . . . . . . . . . . . . . . . . . . . . . .+220°C
ESD Rating, MIL-STD-883B . . . . . . . . . . . . . . . . . . . . . 4 kV
EFT Rating, IEC1000-4-4 . . . . . . . . . . . . . . . . . . . . . . . 2 kV
*Stresses above those listed under Absolute Maximum Ratings may cause perma-
nent damage to the device. This is a stress rating only; functional operation of the
device at these or any other conditions above those listed in the operational
sections of this specification is not implied. Exposure to absolute maximum ratings
for extended periods of time may affect device reliability.
Power Dissipation 14-Lead SOIC . . . . . . . . . . . . . . . 800 mW
θ
, Thermal Impedance . . . . . . . . . . . . . . . . . . . 120°C/W
JA
ORDERING GUIDE
Model Temperature Range Package Description Package Option
ADM488AR –40°C to +85°C 8-Lead Narrow Body (SOIC) SO-8
ADM488AN –40°C to +85°C 8-Lead Plastic DIP N-8
ADM489AN –40°C to +85°C 14-Lead Plastic DIP (Narrow) N-14
ADM489AR –40°C to +85°C 14-Lead Narrow Body (SOIC) R-14
ADM489ARU –40°C to +85°C 16-Lead Thin Shrink Small Outline Package (TSSOP) RU-16
–3–REV. 0
Page 4
ADM488/ADM489
ADM488 PIN FUNCTION DESCRIPTIONS
Pin Mnemonic Function
1V
CC
Power Supply, 5 V ± 10%.
2 RO Receiver Output. When A > B by 200 mV,
RO = high. If A < B by 200 mV, RO = low.
3 DI Driver Input. A logic Low on DI forces Y low
and Z high while a logic High on DI forces Y
high and Z low.
4 GND Ground Connection, 0 V
5 Y Noninverting Driver, Output Y
6 Z Inverting Driver, Output Z
7 B Inverting Receiver Input B
8 A Noninverting Receiver Input A
ADM489 PIN FUNCTION DESCRIPTIONS
DIP/SOIC TSSOP
Pin Pin Mnemonic Function
1, 8, 13 2, 9, 10, NC No Connect. No connections
13, 16 are required to this pin.
2 3 RO Receiver Output. When
enabled if A > B by 200 mV
then RO = high. If A < B by
200 mV then RO = low.
34RE Receiver Output Enable. A
low level enables the receiver
output, RO. A high level
places it in a high impedance
state.
4 5 DE Driver Output Enable. A
high level enables the driver
differential outputs, Y and Z.
A low level places it in a high
impedance state.
5 6 DI Driver Input. When the
driver is enabled, a logic Low
on DI forces Y low and Z
high, while a logic High on
DI forces Y high and Z low.
6, 7 7, 8 GND Ground Connection, 0 V
9 11 Y Noninverting Driver
Output Y
10 12 Z Inverting Driver Output Z
11 14 B Inverting Receiver Input B
12 15 A Noninverting Receiver
Input A
14 1 V
CC
Power Supply, 5 V ± 10%.
PIN CONFIGURATIONS
8-Lead DIP/SO
V
RO
GND
CC
DI
1
ADM488
2
TOP VIEW
(Not to Scale)
3
4
8
A
7
B
6
Z
5
Y
14-Lead DIP/SO
1
NC
2
RO
3
RE
DE
4
(Not to Scale)
DI
5
6
GND
GND
7
NC = NO CONNECT
ADM489
TOP VIEW
14
V
CC
13
NC
12
A
11
B
Z
10
Y
9
NC
8
16-Lead TSSOP
1
V
CC
2
NC
3
RO
4
RE
5
(Not to Scale)
6
DI
7
GND
8
GND
NC = NO CONNECT
ADM489
TOP VIEW
16
NC
15
A
14
B
13
NC
ZDE
12
Y
11
NC
10
NC
9
–4–
REV. 0
Page 5
Test Circuits
ADM488/ADM489
V
CC
DE
A
S1 S2
B
R
L
C
L
V
OUT
R
V
OD
R
V
OC
0V OR 3V
DE IN
Figure 1. Driver Voltage Measurement Test Circuit
375V
V
60V
OD3
375V
V
TST
Figure 2. Driver Enable/Disable Test Circuit
+3V
DE
Y
DI
D
Z
Figure 3. Driver Voltage Measurement Test Circuit 2
V
+1.5V
–1.5V
S1
RE IN
RE
R
C
L
V
OUT
CC
L
S2
Figure 4. Receiver Enable/Disable Test Circuit
A
C
L1
RL
DIFF
B
C
L2
RO
R
RE
Figure 5. Driver/Receiver Propagation Delay Test Circuit
–5–REV. 0
Page 6
ADM488/ADM489
Switching Characteristics
3V
+VO
–VO
0V
0V
B
VO
A
1/2VO
90% POINT
10% POINT
T
1.5V
PLH
T
T
SKEW
R
1.5V
T
PHL
T
90% POINT
10% POINT
T
F
SKEW
Figure 6. Driver Propagation Delay, Rise/Fall Timing
A–B
RO
0V
T
PLH
1.5V 1.5V
0V
T
PHL
V
OH
V
OL
T
T
1.5V
LZ
HZ
A, B
A, B
1.5VDE
T
ZL
2.3V
T
ZH
2.3V
Figure 8. Driver Enable/Disable Timing
RE
R
R
0V
1.5V 1.5V
T
ZL
1.5V
O/P LOW
T
ZH
O/P HIGH
1.5V
T
LZ
T
HZ
+ 0.5V
V
OL
VOH – 0.5V
+ 0.5V
V
OL
VOH – 0.5V
3V
0V
V
OL
V
OH
0V
3V
0V
V
OL
V
OH
Figure 7. Receiver Propagation Delay
–6–
Figure 9. Receiver Enable/Disable Timing
REV. 0
Page 7
Typical Performance Characteristics–
LOG FREQUENCY (0.15–30) – MHz
0.3 0.6
1361030
80
0
70
40
30
20
10
60
50
LIMIT
dBµV
ADM488/ADM489
40
35
30
25
20
15
10
OUTPUT CURRENT – mA
5
0
0 0.5 2.51.0 1.5 2.0
OUTPUT VOLTAGE – Volts
Figure 10. Receiver Output Low
Voltage vs. Output Current
0
–10
–20
–30
–40
–50
–60
OUTPUT CURRENT – mA
–70
–80
–90
0
0.5 5.01.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
OUTPUT VOLTAGE – Volts
0
–5
–10
–15
OUTPUT CURRENT – mA
–20
3.4 3.6 5.03.8 4.0 4.2 4.4 4.6 4.8
OUTPUT VOLTAGE – Volts
Figure 11. Receiver Output High
Voltage vs. Output Current
80
70
60
50
40
30
20
OUTPUT CURRENT – mA
10
0
0 0.5 4.51.0 1.5 2.0 3.0 3.5 4.02.5
OUTPUT VOLTAGE – Volts
90
80
70
60
50
40
30
OUTPUT CURRENT – mA
20
10
0
0.5 3.01.0 1.5 2.0 2.5
0
OUTPUT VOLTAGE – Volts
Figure 12. Driver Output Low
Voltage vs. Output Current
T
100
T
90
T
10
0%
RO
DI
10dB/DIV
Figure 16. Driver Output Waveform
and FFT Plot Transmitting @ 150 kHz
Figure 13. Driver Output High
Voltage vs. Output Current
100
90
10
0%
500kHz/DIV0 5MHz
Figure 14. Driver Differential Output
Voltage vs. Output Current
80
70
60
50
40
dBµV
30
20
10
0
30 200
FREQUENCY – MHz
LIMIT
Figure 17. Radiated Emissions
–7–REV. 0
Figure 15. Driving 4000 ft. of Cable
Figure 18. Conducted Emissions
Page 8
ADM488/ADM489
GENERAL INFORMATION
The ADM488/ADM489 is a ruggedized RS-485 transceiver that
operates from a single +5 V supply.
It contains protection against radiated and conducted interference.
It is ideally suited for operation in electrically harsh environ-
ments or where cables may be plugged/unplugged. It is also
immune to high RF field strengths without special shielding
precautions. It is intended for balanced data transmission and
complies with both EIA Standards RS-485 and RS-422. It contains a differential line driver and a differential line receiver, and
is suitable for full duplex data transmission.
The input impedance on the ADM488/ADM489 is 12 kΩ,
allowing up to 32 transceivers on the differential bus.
The ADM488/ADM489 operates from a single +5 V ± 10%
power supply. Excessive power dissipation caused by bus contention or by output shorting is prevented by a thermal shutdown circuit. This feature forces the driver output into a high
impedance state if, during fault conditions, a significant temperature increase is detected in the internal driver circuitry.
The receiver contains a fail-safe feature that results in a logic
high output state if the inputs are unconnected (floating).
A high level of robustness is achieved using internal protection
circuitry, eliminating the need for external protection components such as tranzorbs or surge suppressors.
Low electromagnetic emissions are achieved using slew limited
drivers, minimizing interference both conducted and radiated.
The ADM488/ADM489 can transmit at data rates up to
250 kbps.
A typical application for the ADM488/ADM489 is illustrated in
Figure 19. This shows a full-duplex link where data may be
transferred at rates up to 250 kbps. A terminating resistor is
shown at both ends of the link. This termination is not critical
since the slew rate is controlled by the ADM488/ADM489 and
reflections are minimized.
The communications network may be extended to include
multipoint connections as shown in Figure 25. Up to 32 transceivers may be connected to the bus.
Tables I and II show the truth tables for transmitting and
receiving.
Table I. Transmitting Truth Table
Inputs Outputs
RE DE DI Z Y
X1101
X1010
0 0 X Hi-Z Hi-Z
1 0 X Hi-Z Hi-Z
X = Don’t Care.
Table II. Receiving Truth Table
Inputs Output
RE DE A-B RO
00≥ +0.2 V 1
01≤ +0.2 V 0
0 0 Inputs O/C 1
1 0 X Hi-Z
X = Don’t Care.
EFT TRANSIENT PROTECTION SCHEME
The ADM488/ADM489 uses protective clamping structures on
its inputs and outputs that clamp the voltage to a safe level and
dissipates the energy present in ESD (Electrostatic) and EFT
(Electrical Fast Transients) discharges.
FAST TRANSIENT BURST IMMUNITY (IEC1000-4-4)
IEC1000-4-4 (previously 801-4) covers electrical fast-transient/
burst (EFT) immunity. Electrical fast transients occur as a
result of arcing contacts in switches and relays. The tests simulate the interference generated when, for example, a power relay
disconnects an inductive load. A spark is generated due to the
well known back EMF effect. In fact, the spark consists of a
burst of sparks as the relay contacts separate. The voltage appearing on the line, therefore, consists of a burst of extremely
fast transient impulses. A similar effect occurs when switching
on fluorescent lights.
+5V
0.1mF
V
CC
RE
RO
ADM488
DI
DE
D
A
R
B
RS-485/RS-422 LINK
Z
Y
Figure 19. ADM488/ADM489 Full-Duplex Data Link
–8–
Y
Z
B
A
+5V
V
CC
D
ADM489
R
GNDGND
0.1mF
DE
DI
RO
RE
REV. 0
Page 9
ADM488/ADM489
The fast transient burst test, defined in IEC1000-4-4, simulates
this arcing and its waveform is illustrated in Figure 20. It
consists of a burst of 2.5 kHz to 5 kHz transients repeating at
300 ms intervals. It is specified for both power and data lines.
Four severity levels are defined in terms of an open-circuit voltage as a function of installation environment. The installation
environments are defined as
1. Well-protected
2. Protected
3. Typical Industrial
4. Severe Industrial
V
t
300ms 16ms
V
5ns
50ns
0.2/0.4ms
t
Figure 20. IEC1000-4-4 Fast Transient Waveform
Table III shows the peak voltages for each of the environments.
Table III.
V
(kV) V
PEAK
PEAK
(kV)
Level PSU I-O
1 0.5 0.25
2 1 0.5
32 1
44 2
A simplified circuit diagram of the actual EFT generator is
illustrated in Figure 21.
These transients are coupled onto the signal lines using an EFT
coupling clamp. The clamp is 1 m long and completely surrounds the cable, providing maximum coupling capacitance
(50 pF to 200 pF typ) between the clamp and the cable. High
energy transients are capacitively coupled onto the signal lines.
Fast rise times (5 ns) as specified by the standard result in very
effective coupling. This test is very severe since high voltages are
coupled onto the signal lines. The repetitive transients can often
cause problems, where single pulses do not. Destructive latchup
may be induced due to the high energy content of the transients.
Note that this stress is applied while the interface products are
powered up and are transmitting data. The EFT test applies
hundreds of pulses with higher energy than ESD. Worst case
transient current on an I-O line can be as high as 40 A.
HIGH
VOLTAGE
SOURCE
R
C
C
C
LR
C
D
M
Z
S
50V
OUTPUT
Figure 21. EFT Generator
Test results are classified according to the following:
1. Normal performance within specification limits.
2. Temporary degradation or loss of performance that is selfrecoverable.
3. Temporary degradation or loss of function or performance
that requires operator intervention or system reset.
4. Degradation or loss of function that is not recoverable due to
damage.
The ADM488/ADM489 has been tested under worst case conditions using unshielded cables, and meets Classification 2 at
severity Level 4. Data transmission during the transient condition is corrupted, but it may be resumed immediately following
the EFT event without user intervention.
RADIATED IMMUNITY (IEC1000-4-3)
IEC1000-4-3 (previously IEC801-3) describes the measurement
method and defines the levels of immunity to radiated electromagnetic fields. It was originally intended to simulate the electromagnetic fields generated by portable radio transceivers or
any other device that generates continuous wave radiated electromagnetic energy. Its scope has since been broadened to include
spurious EM energy, which can be radiated from fluorescent
lights, thyristor drives, inductive loads, etc.
Testing for immunity involves irradiating the device with an EM
field. There are various methods of achieving this including use
of anechoic chamber, stripline cell, TEM cell and GTEM cell.
These consist essentially of two parallel plates with an electric
field developed between them. The device under test is placed
between the plates and exposed to the electric field. There are
three severity levels having field strengths ranging from 1 V to
10 V/m. Results are classified as follows:
1. Normal Operation.
2. Temporary Degradation or loss of function that is selfrecoverable when the interfering signal is removed.
3. Temporary degradation or loss of function that requires
operator intervention or system reset when the interfering
signal is removed.
4. Degradation or loss of function that is not recoverable due to
damage.
–9–REV. 0
Page 10
ADM488/ADM489
The ADM488/ADM489 comfortably meets Classification 1 at
the most stringent (Level 3) requirement. In fact, field strengths
up to 30 V/m showed no performance degradation and errorfree data transmission continued even during irradiation.
Table IV.
Level
V/m Field Strength
11
23
310
EMI EMISSIONS
The ADM488/ADM489 contains internal slew rate limiting in
order to minimize the level of electromagnetic interference
generated. Figure 22 shows an FFT plot when transmitting a
150 kHz data stream.
100
90
10dB/DIV
10
0%
500kHz/DIV0 5MHz
CONDUCTED EMISSIONS
This is a measure of noise that is conducted onto the mains
power supply. The noise is measured using a LISN (Linc Impedance Stabilizing Network) and a spectrum analyzer. The test
setup is illustrated in Figure 23. The spectrum analyzer is set to
scan the spectrum from 0 MHz to 30 MHz. Figure 24 shows
that the level of conducted emissions from the ADM488/
ADM489 are well below the allowable limits.
SPECTRUM
ANALYZER
DUT
LISN PSU
Figure 23. Conducted Emissions Test Setup
80
70
60
50
40
dBµV
30
20
10
0
1361030
0.3 0.6
LOG FREQUENCY (0.15–30) – MHz
LIMIT
Figure 22. Driver Output Waveform and FFT Plot Transmitting @ 150 kHz
As may be seen, the slew limiting attenuates the high frequency
components. EMI is therefore reduced, as are reflections due to
improperly terminated cables.
EN55022, CISPR22 defines the permitted limits of radiated
and conducted interference from Information Technology
Equipment (ITE).
The objective is to control the level of emissions, both conducted and radiated.
For ease of measurement and analysis, conducted emissions are
assumed to predominate below 30 MHz, while radiated emissions predominate above this frequency.
Figure 24. Conducted Emissions
–10–
REV. 0
Page 11
ADM488/ADM489
APPLICATIONS INFORMATION
Differential Data Transmission
Differential data transmission is used to reliably transmit data
at high rates over long distances and through noisy environments. Differential transmission nullifies the effects of ground
shifts and noise signals, which appear as common-mode voltages on the line. Two main standards are approved by the
Electronics Industries Association (EIA), which specify the
electrical characteristics of transceivers used in differential
data transmission.
The RS-422 standard specifies data rates up to 10 MBaud and
line lengths up to 4000 ft. A single driver can drive a transmission line with up to 10 receivers.
In order to cater to true multipoint communications, the RS485 standard was defined. This standard meets or exceeds all
the requirements of RS-422 and also allows for up to 32 drivers
and 32 receivers to be connected to a single bus. An extended
common-mode range of –7 V to +12 V is defined. The most
significant difference between RS-422 and RS-485 is the fact
that the drivers may be disabled thereby allowing more than
one (32, in fact) to be connected to a single line. Only one
driver should be enabled at a time but the RS-485 standard
contains additional specifications to guarantee device safety in
the event of line contention.
Table V. Comparison of RS-422 and RS-485 Interface Standards
Cable and Data Rate
The transmission line of choice for RS-485 communications is a
twisted pair. Twisted pair cable tends to cancel common mode
noise and also causes cancellation of the magnetic fields generated by the current flowing through each wire, thereby reducing
the effective inductance of the pair.
The ADM488/ADM489 is designed for bidirectional data communications on multipoint transmission lines. A typical application showing a multipoint transmission network is illustrated in
Figure 25. An RS-485 transmission line can have as many as
32 transceivers on the bus. Only one driver can transmit at
a particular time but multiple receivers may simultaneously
be enabled.
As with any transmission line, it is important that reflections are
minimized. This may be achieved by terminating the extreme
ends of the line using resistors equal to the characteristic impedance of the line. Stub lengths of the main line should also be
kept as short as possible. A properly terminated transmission
line appears purely resistive to the driver.
Specification RS-422 RS-485
Transmission Type Differential Differential
Maximum Data Rate 10 MB/s 10 MB/s
Maximum Cable Length 4000 ft. 4000 ft.
Minimum Driver Output Voltage ±2 V ±1.5 V
Driver Load Impedance 100 Ω 54 Ω
Receiver Input Resistance 4 kΩ min 12 kΩ min
Receiver Input Sensitivity ± 200 mV ±200 mV
Receiver Input Voltage Range –7 V to +7 V –7 V to +12 V
Number of Drivers/Receivers Per Line 1/10 32/32
RT RT
D
R
RR
DD
D
R
Figure 25. Typical RS-485 Network
–11–REV. 0
Page 12
ADM488/ADM489
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
0.1574 (4.00)
0.1497 (3.80)
0.0098 (0.25)
0.0040 (0.10)
SEATING
PLANE
0.210 (5.33)
MAX
0.160 (4.06)
0.115 (2.93)
0.022 (0.558)
0.014 (0.356)
8-Lead Narrow Body (SOIC)
(SO-8)
0.1968 (5.00)
0.1890 (4.80)
8
5
0.2440 (6.20)
41
0.2284 (5.80)
PIN 1
0.0500
(1.27)
BSC
0.0688 (1.75)
0.0532 (1.35)
0.0192 (0.49)
0.0138 (0.35)
0.0098 (0.25)
0.0075 (0.19)
8-Lead Plastic DIP
(N-8)
0.430 (10.92)
0.348 (8.84)
8
14
PIN 1
0.100
(2.54)
BSC
5
0.280 (7.11)
0.240 (6.10)
0.060 (1.52)
0.015 (0.38)
0.070 (1.77)
0.045 (1.15)
0.130
(3.30)
MIN
SEATING
PLANE
0.325 (8.25)
0.300 (7.62)
0.0196 (0.50)
0.0099 (0.25)
8°
0°
0.0500 (1.27)
0.0160 (0.41)
0.015 (0.381)
0.008 (0.204)
x 45°
0.195 (4.95)
0.115 (2.93)
0.210 (5.33)
MAX
0.160 (4.06)
0.115 (2.93)
0.1574 (4.00)
0.1497 (3.80)
0.0098 (0.25)
0.0040 (0.10)
SEATING
14-Lead Plastic DIP
(N-14)
0.795 (20.19)
0.725 (18.42)
14
17
PIN 1
0.022 (0.558)
0.014 (0.356)
0.100
(2.54)
BSC
0.070 (1.77)
0.045 (1.15)
8
0.280 (7.11)
0.240 (6.10)
0.060 (1.52)
0.015 (0.38)
14-Lead Narrow Body (SOIC)
(R-14)
0.3444 (8.75)
0.3367 (8.55)
PLANE
14 8
PIN 1
0.0500
0.0192 (0.49)
(1.27)
0.0138 (0.35)
BSC
0.2440 (6.20)
71
0.2284 (5.80)
0.0688 (1.75)
0.0532 (1.35)
0.130
(3.30)
MIN
SEATING
PLANE
0.0099 (0.25)
0.0075 (0.19)
0.325 (8.25)
0.300 (7.62)
0.015 (0.381)
0.008 (0.204)
0.0196 (0.50)
0.0099 (0.25)
8°
0°
0.0500 (1.27)
0.0160 (0.41)
0.195 (4.95)
0.115 (2.93)
x 45°
C3160–12–9/97
16-Lead Thin Shrink Small Outline Package (TSSOP)
(RU-16)
0.201 (5.10)
0.193 (4.90)
16 9
0.177 (4.50)
0.006 (0.15)
0.002 (0.05)
SEATING
PLANE
0.169 (4.30)
1
PIN 1
0.0256
(0.65)
BSC
0.0118 (0.30)
0.0075 (0.19)
8
0.256 (6.50)
0.246 (6.25)
0.0433
(1.10)
MAX
0.0079 (0.20)
0.0035 (0.090)
8°
0°
0.028 (0.70)
0.020 (0.50)
–12–
PRINTED IN U.S.A.
REV. 0
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