TIA/EIA-422 Electrical Characteristics of Balanced Voltage Digital
Interface Circuits
[RS422 Description] [RS422 ICs
] [Standard Organizations]
[RS449 Cabling] [RS422 Pull-Up/Pull-Down Resistors] [OEM
RS422 Converter Devices ]
[Home]
EIA/TIA-422 defines a Balanced (differential) interface;
specifying a single, unidirectional driver with multiple receivers
(up to 32). RS-422 will support Point-to-Point, and Multi-Drop circuits,
but not Multi-Point [EIA485].
EIA-485 devices may be used in 422 circuits, but EIA-422 may not be
used in 485 circuits (because of the lack of an Enable line). EIA422
is the differential "brother" to EIA423. One application note indicated
that the combination of cable length (in meters) and data
signaling rate (in bps) for RS422 should not exceed 108.
The example provided a maximum speed of 200kbps with a maximum cable
length of 500 meter [500 x 200,000]. An EIA-422 driver can support up
to 10 loads, at 4K W per load. |
Cabling standards are listed lower down the page. The common name for this interface is RS422.
TIA/EIA-422: Electrical Characteristics of Balanced Voltage
Digital Interface Circuits
TIA/EIA-485: Electrical Characteristics of Generators and
Receivers for Use in Balanced Digital Multipoint Systems
Electronic Industries Alliance, EIA was disbanded & ceased operations in 2011.
Telecommunications Industry Association {TIA}, [www.tiaonline.org]
V.11: Electrical characteristics for balanced double-current interchange circuits operating at data signalling rates up to 10 Mbit/s
ITU, International Telecommunication Union, http://www.itu.int
FED STD 1030A is identical to TIA/EIA-422-B. It is intended for
United States, non-military government use.
FED STD 1020A is identical to TIA/EIA-423-B. It is intended for
the United States, non-military government use.
IC Interface Vendors:
Dallas Semiconductor Corp see Maxim
Exar {RS-422 Differential Driver/Receiver IC Manufacturer}
Linear Technology {EIA422-EIA485 Transceiver-Driver-Receiver ICs}
Maxim {RS232-RS485-RS422 IC Manufacturer}
National Semiconductor {RS422 Differential Bus Transceiver-Receiver-Driver}
ON Semiconductor {EIA485 Transceiver-EIA562-EIA422/EIA423 IC Manufacturer}
STMicroelectronics {EIA422 components}
Texas Instruments 'TI' {RS-232/RS-422/RS-423/RS-422 Diff Driver/Receiver ICs}
Memory Chip IC Manufacturers
Processor Chip
Manufacturers
Glue Logic IC
Manufacturers
The Pullup/Down Resistors (Idle-line failsafe) are used to keep the +/- inputs of the Receiver(s) inputs at a minimum of 200mV differential. The resistors are normally required once the system has reached it's quiescent state, when no drivers are driving the bus. Only one end of the bus requires the resistor network.
The resistor values are dictated by four factors: The input impedance of
the receivers (between 5K and 90K ~ check the data sheet), the number of
loads, the termination resistance
60 ohms (120 ohms per side), and the required (turn-on) current of the
receivers.
Many (on-line) App-notes use 12K ohms as an input impedance, 60 ohms (as
a termination), 3.5 mA as the minimum 'load' current, and 10 loads.
Using these values {Check the data sheets for the real values!}:
..... Number of loads (10) x 12KW ~
1200W {That's ten 12Kohm resistors in
parallel, 12K//10 loads}
......Line Termination ~ 60 ohms {120 ohms at each side of the
link, in parallel, 120//120}
......Taking 1200 in parallel with 60 ohms gives 57 ohms
......Turn-On current ~ 3.5 mA {check the data sheet for the
device used}
The required load is 5volts / 3.5mA, which results in a load impedance of
(around) 1428 ohms. Subtract 57W which is
already present leaves; 1371W.
Placing half on the +5 volts line and the other on the ground line, gives
675W per resistor / per supply.
The nearest 5% standard value is
680W placed between both the 'A' line
and +V connection and the 'B' line and the GND connection will produce
< 3.5 mA (turn-on current}
RS422 and RS485 do not define cabling or connector information. RS449 and RS530 [listed below] are two common cabling specifications which are used with the RS422/485 electrical standards. Use 24 AWG twisted pair copper wire with 16pF/ft for cables. Maximum cable length is determined by the combination of cable length (in meters) and data signaling rate (in bps). RS422 should not exceed 108 for length x bps. The example provided a maximum speed of 200kbps with a maximum cable length of 500 meter [500 x 200,000]. Charts of Cable Data Rate vs Cable Length.
EIA/TIA-449; General Purpose
37-Position Interface for Data terminal Equipment and Data
Circuit-Terminating Equipment Employing Serial binary Data
Interchange
TIA-449 is a serial mechanical interface standard for transmission of balanced and
unbalanced signals between a variety of higher-end computer, media, and
multimedia peripherals. EIA-449 allows a maximum data rate of 10 Mbit/s
and uses a 37-pin or 9-pin connector.
EIA/TIA-530; High Speed 25-Position
Interface for Data Terminal Equipment and Data Circuit-Terminating
Equipment, Including Alternative 26-Position Connector
EIA-530 is a replacement for EIA-449 that uses a DB-25 (EIA-232-D) connector instead of a 37-pin
connector, while keeping the most important electrical signals intact.
EIA-530 is to be used in conjunction with EIA-422-A.
RS-530, 25pin pinout
RS-449, 37pin pinout
RS-449, 9pin pinout
Data Rate | Cable Length |
2 Mb/sec | 15.24 Meters |
1 Mb/sec | 30.48 Meters |
512 Kb/sec | 60.96 Meters |
256 Kb/sec | 121.92 Meters |
128 Kb/sec | 243.84 Meters |
56 K | 487.68 Meters |
1.2 Kb/sec | 914.40 Meters |
RS422 pinout is not defined in the standard, any pin out table found for RS422 is non-standard.
I/O Converter Vendors;
Acces I/O Products Inc. {RS422 to
RS232 Converter Devices}
B&B electronics {422 Converter/Optically Isolated 485 Converter/232 to 422 Converters}
EQUIP'TRANS {V11/V24/20mA to RS-485 Converter Devices}
KK Systems Ltd. {RS232-RS422/RS485 Isolated Interface Converter}
Lascomm {Fiber Converter EIA232 to RS485 Converters - RS232 to V.35/X21}
Patton Electronics Co. {RS-232 to RS-422/449 (V.36) Interface Converter}
Telebyte {RS422 and many Converter types}
Normally EIA422 and 423 systems may not be connected together. EIA-449
cabling of RS422 sends and receives data as differential pairs and
control signal as single-ended, but for 423 cabling it sends and receives
single-ended data and control signals. Receiving the single ended signal
in 423 is accomplished by grounding the 'B' side of the differential
receiver at the connector.
So if the system follows the EIA-449 (cabling) specification than one (B)
side of the differential receiver of the 423 side will be grounded at the
connector forcing the differential driver on the 422 side to drive
ground. The EIA422 side also uses a termination resistor between the ends
of its differential receiver, providing a serious 120 ohm short to ground
for the 423 driver.
If the systems were to be connected together (with out regard for RS499)
than the system would revert to EIA423 (single-ended) distance and data
rate ~ Only because the driver on the RS423 side is single ended, while
the receiver on the RS422 side would receive the single-ended 423 signal
and ground on its differential pair. How ever because 423 and 422 use the
same receiver chip; going from 422 to 423 provides a differential path.
Design Note; Signal inversion is easily accomplished by transposing the EIA423 lines [signal and ground] at the RS422 receiver.
Navigation: Engineering Home > Interface Buses > Cabled Interface Standards > TIA-422 Interface
Home | |||||||
Distributors | Components | Equipment | Software | Standards | Buses | Design | Reference |