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INFORMATION
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NOVEMBER 1993
IC107A
RS-232↔RS-422/485 Converter
(Data Only)
232
↔
422/485 CONVERTER
DATA ONLY
RX TX PWR
2
RS-232↔RS-422/485 Converter (Data Only)
FEDERAL COMMUNICATIONS COMMISSION
RADIO FREQUENCY INTERFERENCE STATEMENT
This equipment generates, uses and can radiate radio frequency energy
and if not installed and used properly, that is in strict accordance with the
manufacturer’s instructions, may cause interference to radio communication.
It has been tested and found to comply with the limits for a Class A
computing device in accordance with the specifications in Subpart J of
Part 15 of FCC rules, which are designed to provide reasonable protection
against such interference when operated in a commercial environment.
Operation of this equipment in a residential area is likely to cause
interference, in which case the user at his own expense will be required
to take whatever measures may be required to correct the interference.
Any other trademarks mentioned in this manual are acknowledged to be the property
of the trademark owners.
3
Contents
Contents
Section Page
1. Specifications ................................................................................................ 4
2. Introduction.................................................................................................. 5
2.1 Typical Applications................................................................................ 5
3. Installation .................................................................................................... 7
4. Operation...................................................................................................... 9
4.1 RS-232 Circuitry....................................................................................... 9
4.2 RS-422/485 Circuitry .............................................................................. 11
Appendix: Connector Pinning ........................................................................ 12
4
RS-232↔ RS-422/485 Converter (Data Only)
Speed — Up to 64 Kbps
Maximum Distance — 4000 feet
(1219 m)
Operation — 4-wire, full-duplex;
point-to-point or multipoint; userconfigurable DTE/DCE RS-232 port
Leads supported — RS-232 port: 18, 20; RS-422/485 port: TXA, TXB,
RXA, RXB
Indicators — (3) LEDs: TX, RX,
POWER
Flow control — Transparent to flow
control
Interface — Asynchronous RS-422/485;
asynchronous RS-232
Connectors — (1) DB25 female;
(1) four-pin terminal block
Temperature — Operating: 32° to
122° F(0° to 50° C); Storage: -4° to
158° F (-20° to 70° C)
Humidity — 0 to 95% noncondensing
Mean Time
Between Failures
(MTBF) — 200,000 hours
Power — Primary: 115 VAC/60 Hz
model, @ 70 mA, or 230 VAC/50 Hz
model, @ 35 mA; Secondary: 17 volt
center tapped, 0.7 ma; Connector
pinning:
Pin Function
1 Frame ground
2 Secondary
3 Secondary
4 Signal ground
(center tap)
Size — Standalone unit: 1.8"H x
5.5"W x 8.5"D (4.6 x 14x 22 cm);
Rackmount card: 4.7"H x 7.4"W
(12 x 19 cm)
Weight — Standalone unit: 1 lb. (0.5
kg); wallmount power supply: 0.5 lb.
(0.2 kg); Rackmount card: 0.5 lb.
(0.2 kg)
1. Specifications
5
Chapter 2: Introduction
The RS-232↔RS-422/485 Converter
(Data Only) allows your RS-232
and RS-422/485 equipment to
communicate. It operates over
4-wire lines, in full-duplex operation.
A four-wire terminal block on the
RS-422/485 port makes installation
easy. And this interface converter is
flexible: it can work in either pointto-point or multidrop-network
applications. The RS-232 interface
is user-selectable as either Data
Terminal Equipment (DTE) or Data
Communications Equipment (DCE)
for a wide range of applications.
The converter is available in either
standalone or rackmount card units.
2.1 Typical Applications
Figs. 2-1 and 2-2 illustrate typical
applications using the RS-232↔RS422/485 converter. The connections
shown are for the RS-422/485 port.
A resistor shown in the circuit
indicates that the termination
resistor has been selected via switch
S2. (Please note that although
Fig. 2-2 shows only two converters
networked together, up to 64 units
can be connected in a multipoint
network).
Both figures.show the signal
flow for the RS-232↔RS-422/485
Converter in full-duplex operation
for both point-to-point and multipoint applications. (Direction of
signal flow is indicated by arrows).
Also shown are the locations of the
indicator LEDs.
2. Introduction
R x B
T x A
T x A
R x A
RS-232
Device
RS-422/485
Device
T x B
T x B
R x B
R x A
Terminated
RS-232 <—> RS-422/485
Interface Converter
Fig. 2-1. 4-Wire Point-to-Point Application
(Full-Duplex Operation).
6
RS-232↔ RS-422/485 Converter (Data Only)
PC
RS-232
↔
RS-422/485
INTERFACE CONVERTER
+
-
+-
+-
+-
DATA LOGGER BAR-CODE
READER
LATHE
Fig. 2-2. 4-Wire Multipoint Application
(Full-Duplex Operation).
7
Chapter 3: Installation
Here's how to install the RS-232↔
RS-422/485 converter. Refer to Fig.
3-1 for the location of components
on the unit's circuit board.
Follow these steps to configure the
converter for your application:
1. Set the unit's RS-232 port for your
application by configuring it for
either DTE or DCE operation.
For your RS-232 port to appear as
a DTE device, put the DIP-shunt
jumper (shown in Fig. 3-1) in
socket XW1B. For the RS-232
port to appear as a DCE device,
put the DIP-shunt jumper in
socket XW1A.
2. Set strap W15 to select how the
converter's RS-422/485 driver is
enabled. If you place the jumper
across W15 Pins B and C, the RS422/485 driver is always enabled.
If W15 is in the factory-set default
position (jumper across Pins A
and B), you can use W18 to
configure the RS-422/485 driver
to be enabled by either DTR or
RTS on the RS-232 interface.
For DTR to enable the driver,
leave W18 in the default position
(jumper across Pins A and B). For
RTS to enable the driver, place
the jumper across Pins B and C.
6
R17
R18
CR12
CR11
CR7
CR10
CR8
CR9
CR17
CR19
CR18
CR20
TB1
J3
CR22
CR21
TXA TXB RXA RXB
P1
W7
S2 0N
UNTERM TERM
13
J1
C16
1
DCE
XW1A
8
7
5
4
3
2
1
C7 C6 C8
C21 C22
C11
U5
C14
U6
C17
VR1
C10
R6
R7
R32
DTE
XW1A
Q4 C9
U1
C12
A B C
W18
C1
U2
C15
U3
Q3
R8
C23
A B C
W15
R39
U4
U8
TX
CR3
PWR
CR5
RX
CR4
S1
DEFAULT
POSITION
"UNTERM"
Fig. 3-1. The RS-232↔ RS-422/485 Converter's Circuit Board.
RS-232
Connector
RS-422/485.
Connector
3. Installation
DTE
XW1B
DCE
XW1A
8
RS-232↔ RS-422/485 Converter (Data Only)
3. Some applications require the
RS-422/485 interface to be
terminated. A resistor network
provides this termination on the
converter at the RS-422/485
input receiver pins (RXA and
RXB). You set terminated or
unterminated operation through
Switch S2 (see Fig. 3-1).
When S2 is placed in the
"TERM" position, the resistor
network is connected across
the line, and the RS-422/485
interface is terminated. When
S2 is placed in the "UNTERM"
position, no connection to the
resistor network is made, and the
interface is not terminated.
4. Component W7 can be set to tie
signal ground to frame ground.
The position is left open at the
factory. If you want to connect
signal ground to frame ground,
we recommend that you solder
a 100 Ohm, 0.5 Watt resistor in
location W7. A wire jumper can
also be used; however, care must
be taken to ensure that groundloop currents are limited to
acceptable levels. Otherwise the
converter could sustain damage
due to voltage differences
between the RS-232 and RS422/485 interfaces.
After you complete these steps,
attach the cables from your RS-232
and RS-422/485 devices to the
appropriate connectors on the
converter and power up all three
devices.
You're ready to go.
9
Chapter 4: Operation
4.1 RS-232 Circuitry
The RS-232 side of the converter is
composed of the RS-232 drivers and
receivers, the delay circuitry, and
other circuitry necessary to operate
the RS-232 control lines.
Data traveling from the RS-232
interface to the RS-422/485 interface:
When the RS-232 port is configured
as DCE (see Fig. 4-1), data received
on RS-232 Pin 2 (TD) will be
transmitted out through TXA and
TXB on the RS-422/485 port. For
this transmission, RTS (or DTR,
depending on the position of W18)
must be asserted. In other words,
before you can send any data
through the converter from the RS232 side to the RS-422/485 side, one
of these conditions must be met:
Either (1) you must assert RTS/DTR
and then receive CTS true (ask for
and then be given permission to
send), or (2) the converter must be
set in the mode where the RS422/485 driver is always enabled
(W15 set to the B and C position).
In DTE operation (see Fig. 4-2), Pin
8 (CD) performs the same function
as RTS/DTR did for DCE; Pin 8 asks
for permission to send. Again, you
can constantly enable the RS422/485 driver by setting the W15
jumper in the B and C position.
4. Operation
TD
DTR
RTS
CTS
DSR
RD
CD
ON
C
B
A
TX
RX
RXA
RXB
C
B
A
W15
ENABLE
TXA
TXB
W18
PIN 2
PIN 20
PIN 4
PIN 5
PIN 6
PIN 3
PIN 8
Fig. 4-1 Block Diagram of Converter Functions in DCE Mode.
RS-232
side
RS-422/485
side
10
RS-232↔ RS-422/485 Converter (Data Only)
Fig. 4-2 Block Diagram of Converter Functions in DTE Mode
RD
CD
RTS
TD
DTR
ON
TX
RX
RXA
RXB
C
B
A
W15
TXA
TXB
CTS
DSR
}
UNUSED
PIN 3
PIN 8
PIN 4
PIN 2
PIN 20
PIN 5
PIN 6
Data going from the RS-422/485
interface to the RS-232 interface: When
the RS-232 interface is configured as
DCE, data received on the RXA and
RXB pins of the RS-422/485 port
will be transmitted out Pin 3 (RXD)
of the RS-232 interface.
When the RS-232 interface is
configured as DTE, data received
on RXA and RXB pins of the RS-422
/485 interface will be sent out Pin 2
(TXD) of the RS-232 interface
For more on the RS-232 pinning,
see the Appendix of this manual.
RS-232
side
RS-422/485
side
11
Chapter 4: Operation
4.2 RS-422/485 Circuitry
The RS-422/485 side of the
converter is made up of the driver,
receiver and line-termination
networks. Switch S2 has been
provided to allow the user to either
select the termination network for
the receiver to be connected to the
line (terminated), or left
unconnected (unterminated).
Having the line terminated will
reduce distortion and improve
the overall signal quality in most
applications. For point-to-point
systems where only two devices are
connected to the line, each device
should have the termination network connected to the line. In
multipoint applications, only the
two devices at the extreme ends of
the line should have the termination
network connected to the line. If
any of the other converters were
configured as "terminated," the
amount of signal distortion would
increase and probably cause errors
in the data being transmitted. For
more on the RS-422/485 connector
pinning, see the Appendix.
12
RS-232↔ RS-422/485 Converter (Data Only)
Table A-1. RS-232 Pinning Chart
Pin1 — Frame Ground Connects the converter's frame ground to the
frame ground of the RS-232 device.
Pin 2 — TD When the converter is set to DCE, data is received
on Pin 2 and the TX LED lights up when Pin 2 is a
"space"(logical zero). When the converter is set for
DTE, data is output on Pin 2, in which case the RX
LED lights up when Pin 2 is a "space".
Pin 3 — RD When the converter is set for DCE, data is output
on Pin 3. The RX LED lights up when Pin 3 is a
"space". When the converter is set for DTE, data is
received on Pin 3 and the TX LED lights up when
Pin 3 is a "space".
Pin 4 — RTS When the converter is set for DCE, RTS is an input
which turns on the RS-422/485 driver when true.
When the converter is set for DTE, RTS is always
an output and is always true. (In DTE mode, CD
controls the RS-422/485 driver.)
Pin 5 — CTS When the converter is set for DCE, CTS is an
output that follows the RTS/DTR input. When the
converter is set for DTE, CTS is not used.
Pin 6 — DSR When the converter is set for DCE, DSR is true.
When the converter is set for DTE, DSR is not
used.
Pin 7 — Signal Ground Connects the circuit ground of the converter to the
circuit ground of the RS-232 device.
Pin 8 — CD When the converter is configured DCE, CD is
always true (and RTS controls the RS-422/485
driver). When the converter is set for DTE, CD is
an input which turns on the RS-422/485 driver
when true.
Pin 20 — DTR When the converter is set for DTE, Pin 20 is true.
Appendix: Connector Pinning
13
Appendix: Connector Pinning
Table A-2. RS-422/485 Connector Pinning Chart
RS-422/485 Pin Name Description
TXA and TXB Data received by the converter from the RS-232 port is
transmitted out of the unit over twisted-pair wires via these
two outputs. The "TX" LED indicates the state of these two
leads. When the TXA lead is positive with respect to the
TXB lead (a zero is being transmitted), the "TX" LED is lit.
RXA and RXB These are the received data inputs for the RS-422/485 port.
The status of these leads is monitored by the "RX" LED.
When the RXA lead is positive with respect to the RXB lead
(a zero is being received), the "RX" LED is lit.
Fig. A-1. The RS-232 DB25 Female Connector.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
SECONDARY TRANSMITTED DATA
DCE TRANSMITTER SIGNAL ELEMENT TIMING
SECONDARY RECEIVED DATA
RECEIVER SIGNAL ELEMENT TIMING
SECONDARY REQUEST TO SEND
DATA TERMINAL READY
SIGNAL QUALITY DETECTOR
RING INDICATOR
DATA SIGNAL RATE SELECTOR
DTE TRANSMITTER SIGNAL ELEMENT TIMING
PROTECTIVE GROUND
TRANSMITTED DATA
RECEIVED DATA
REQUEST TO SEND
CLEAR TO SEND
DATA SET READY
SIGNAL GROUND / COMMON RETURN
RECEIVED LINE SIGNAL DETECTOR
+ VOLTAGE
- VOLTAGE
SECONDARY RECEIVED LINE SIGNAL INDICATOR
SECONDARY CLEAR TO SEND
SIGNAL
DESTINATION
PIN
NUMBER
PIN
NUMBER
SIGNAL
DESTINATION
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