2 of 3
9/21/2007
#23685
724-746-5500
blackbox.com
FEATURES
• “Air gap” protects data and equipment
from dangerous electrical problems like
ground loops.
• Supports distances up to 4000 feet
(1219.2 m) between RS-232 and RS-422
units at 19.2 kbps.
• Withstands up to 2500 VAC.
• Bidirectional data conversion.
In a typical application, an opto-isolator connects to an RS-232 PC at one end of a
4000-foot (1219.2-m) RS-422 twisted-pair link. An RS-232
↔
RS-422 interface converter
connects to another RS-232 device at the opposite end of the link.
OVERVIEW
The RS-232
↔
422 Opto-Isolator connects an RS-232 device
to an RS-422 device while protecting against electrical ground
loops that can damage data and equipment.
The opto-isolator translates data signals into bursts of light
that travel across an “air gap” that electricity can’t cross. This
design isolates and protects each end of a data link.
Use opto-isolators wherever an RS-232 device is placed as
far away as 4000 feet (1219.2 m) from an RS-422 device
running at 19.2 kbps. At longer distances, the 19.2-kbps signal
strength weakens significantly and can’t power the opto-
isolator. You can increase the maximum distance rating,
however, by using a larger-gauge wire and slower data
transmission rates.
You can also use opto-isolators when the RS-232 and
RS-422 devices are powered from separate AC sources.
Different AC sources may have different grounding systems
and different ground potential. In these instances, the
possibility of developing an electrical problem—a damaging
surge or spike—increases substantially.
For the most effective protection from ground loops and
electrical disturbances like lightning strikes, use the opto-
isolators and dependable surge protectors.
The opto-isolator has a DTE/DCE switch that’s used to set
the RS-232 device as DTE or DCE.
If the opto-isolator is connected to a DCE device, set the
switch to DTE. If the opto-isolator is connected to a DTE
device, set the switch to DCE. This switch setting determines
the pins from which the opto-isolator will draw its power.
The opto-isolator has a four-screw block connector on one
side (the RS-422 interface) and a DB25 connector (the RS-232
interface) on the other. If you’re connecting the opto-isolator
to a PC or an RS-232 device with a DB25 port, attach the opto-
isolator directly to the RS-232 equipment. If your PC has a DB9
port, however, you’ll need a 6-foot (1.8-m) DB25 M to DB9 F
extension cable. Call Tech Support for details.
The opto-isolator has a few limitations that are worth
noting. First, this unit operates over four wires in full duplex
mode, point-to-point only, so the opto-isolator does not
support loopback testing. Also, two opto-isolators cannot
be used back-to-back in a short-haul modem application.
RS-232 device
RS-232 PC
RS-232
↔
RS-422/485
Converter (Data Only)
(IC107A-R3)
4-wire twisted-pair
cable
RS-232
↔
422 Opto-Isolator
(IC457A-F or IC457A-M)
TECH SPECS
Operation — 4-wire, full duplex, point-to-point
Protocol — Asynchronous
Speed (Maximum) — 19.2 kbps, transparent
Pins Supported — RS-232: TD, RD, SG; RS-422: TXA, TXB, RXA, RXB
Power Consumption — RS-232: 48 mW;
RS-422: 34 mW
RS-232 Voltage Requirements — Minimum: ±3 VDC; Maximum: ±15 VDC
RS-422 Voltage Requirements — Minimum: 2 VDC; Maximum: 6 VDC
Voltage Isolation — Withstands up to 2500 VAC
MTBF — 300,000 hours
Enclosure — High-impact plastic
Interface — RS-232 (DTE or DCE) and RS-422
Connectors — RS-232: (1) DB25 female;
RS-422: (1) 4-screw terminal block
Operating Temperature — 32 to 158°F (0 to 70°C)
Humidity — Up to 95% relative, noncondensing
Power — From both RS-232 and RS-422 interfaces
Size — 0.7"H x 2"W x 2.7"D (1.8 x 5.1 x 6.9 cm)
Weight — 0.1 lb. (<0.1 kg)
