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Model 8322 - RS-232 to RS-485 (4-wire)
Interface Converter DIN Rail Mounted Reference
Manual
I - DESCRIPTION
The Model 8322 RS-232 to RS-485 interface converter allows information
exchange in half-duplex mode over two twisted pair cable. It converts
RS-485 signals to RS-232 signals, bidirectionally, on the DIN rail mounting
system.
The RS-485 standard specified by the Electronic Industries Association
(EIA) relates to the electrical characteristics of the generators and
receivers used in a multipoint system with symmetrical or balanced digital
signals. The RS-485 interface allows the user to control up to 32 devices
in a half duplex via a four wire, two twisted pair line.
The Model 8322 has one RS-232 I/O configured in DCE mode enabling the
reception of data circulating on the receive pair (RS-485 side) or the
transmission of data towards the RS-485 transmit pair. The principle of
the RS-485 4-wire connection involves a half-duplex transmission mode,
i.e. at a given time only one device is authorized to transmit data. Because
this also utilizes a polling procedure it is also referred to as a master-slave
network. The other stations (slaves) must be in stand-by mode, which corresponds
to a 'high impedance' state for each driver. The control of the driver
is generally realized from the RTS signal, although the Model 8322 also
allows control by sampling Transmit Data. This feature is described below
in Section 2. The control of the devices in RS-485 mode requires multipoint
software with polling sequences. The secondary stations controlled by
the master station cannot transmit data unless they are selected.
IMPORTANT : The 4-wire RS-485 link which connects the various equipment
requires a cable with at least 2 twisted pairs, nominal impedance of 120
Ohms and general shielding. The use of a cable with different characteristics
can lead to unreliable operation, especially in case of high data rates
and long distance.
II - OPERATING MODE
2-1 Block Diagram:
The Model 8322 interface converter provides opto isolation between the
RS-232 interface and the RS-485 line by the use of optical couplers. The
transmit data from the RS-232 port can be sent over the RS-485 line only
if the RS-485 driver is in active mode. This active mode can be initialized
either by activation of the RTS signal from the RS-232 port or by detection
of transitions on the transmit data lead (Pin 2 TD). This feature enables
the Model 8322 adapter to support the XON/XOFF flow control from equipment
using only the TD, RD and GND.
2-2 RS-485 4-Wire Connection
The principle of 4-wire connection (2 twisted pairs) enables the management
of up to 32 peripheral devices. The principle of an RS-485 4-wire link
is based upon the use of independent transmission and reception circuits.
Each link requires a terminating load on the ends of the cable. Each Model
8322 includes a switch selectable termination. Those units which are located
at the ends of the cable should have this 120 Ohms termination (RS-485
Standard) selected.
The intermediate secondary stations can use a balancing termination by
connecting a 'pull-up' resistor to the negative line side of the bus and
a 'pull-down' resistor to the positive side of the bus, thereby forcing
a zero condition on the line. The secondary station transmission circuits
present the characteristic of operating in 3 state mode, a high impedance
state during the idle period (period of non data transfer).
The sending of data from one station can be initiated by the incoming
RTS signal (Pin 4) on the RS-232 side going active, or by internal generation
of a data received signal on the RS-232 side. This second method, controlled
by a microprocessor, enables the use of the Model 8322 converter with
a simple 3-wire RS-232 connection and XON/XOFF flow control.
3-2 RS-485 HDX operation mode :
The lack of a control circuit on the RS232 side requires that the Model
8322 take control of managing the driver for transmission of data towards
the RS-485 line. Detecting a start bit sets off the driver immediately
(t0), remaining active until a half-bit following the last stop bit. If
a new start bit is detected during 't2' time, the driver is kept active
until the next character and so on. The internal microprocessor controls
the t0 and t2 times in accordance with the transmission parameters indicated
by the user via the S1 DIP switch (see § 4-3).
III - CONNECTION / CABLING
3-1 RS-232 I/O (DCE mode)
3-2 4-Wire RS-485 I/O
3-3 DIN rail mounting of Model 8322
Top View :
Front View :
IV - SWITCH SETTINGS
4-0 DIP SWITCHES
The Model 8322 incorporates a micro-controller to manage the host protocols
of the interface. Many of the parameters controlling the micro are established
via dip switches. Some of these settings are marked mandatory and should
not be changed. Other switches that are user selectable are appropriately
marked by an X.
4-1 DIP-SWITCH S1 :
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01 : |
Mandatory |
|
01 : |
Mandatory |
 |
010 :
001 :
|
Transmission control with RTS
Transmission control without RTS
Other combinations are not allowed |
 |
0 :
1 : |
Common not connected to Earth by 100 Ohms
Common connected to Earth by 100 Ohms |
4-2 DIP-SWITCH S2 :
4-3 DIP-switch S3
Generally the use of an RS-485 interface implies controlling the Half-duplex
operation mode. The DIP-switch block S1 enables the selection of the operating
mode and data transmission characteristics needed by the microprocessor
in detecting and managing the active phases of the RS-485 transceiver
(see Section 2-3).
Transmitter Configuration S3-1 to S3-3 Baud Rate, S3-4 to S3-5 Byte
Format
| Speed |
S3-1 |
S3-2 |
S3-3 |
| 300bps |
0 |
0 |
0 |
| 600bps |
1 |
0 |
0 |
| 1200bps |
0 |
1 |
0 |
| 2400bps |
1 |
1 |
0 |
| 4800bps |
0 |
0 |
1 |
| 9600bps |
1 |
0 |
1 |
| 19200bps |
0 |
1 |
1 |
| 38400bps |
1 |
1 |
1 |
| Format |
S3-4 |
S3-5 |
| 7 bits, 1 stop, no parity |
0 |
0 |
| 7 bits, 1 stop, with parity |
1 |
0 |
| 7 bits, 2 stops, no parity |
1 |
0 |
| 7 bits, 2 stop, with parity |
0 |
1 |
| 8 bits, 1 stop, no parity |
1 |
0 |
| 8 bits, 1 stop, with parity |
0 |
1 |
| 8 bits, 2 stop, no parity |
0 |
1 |
| 8 bits, 2 stop, with parity |
1 |
1 |
- S3-6 : OFF (ON : not allowed)
- S3-7 : OFF (ON : not allowed)
-
S3-8 : OFF (ON : not allowed)
4-4 Switches and their functions
4-5 Factory settings : Master Mode (dark areas show switch position)
V - SPECIFICATIONS
5-1 Specifications
Interfaces : RS-232 (V.24) and 4-wire RS-485 (EIA)/V28 (CCITT)
Transmission mode : Serial Asynchronous, HDX mode (With/without
RTS signal)
Transmission speed : Transparent to 38,400 BPS
Transmission Code : Transparent
Isolation : Via Opto-Couplers
Power : 115 Vac, 60 Hz standard, 230 Vac, 50 Hz optional
Consumption : 2.5 W Maximum
Dimensions : 3.1" x 1.57" x 3.35" (79 x 40 x
85mm)
Environment : Operating Temperature 0° to 70°C, Storage Temperature
-20° to 70°C, Humidity 10% to 90% No condensation
Approvals: CE marked
VI - SUPPORT
6-1 HELP
If any assistance is required call Bomara Associates at (800)-5BOMARA
or (978)-452-2299.
Technical Support E-Mail: bobr@bomara.com
or use our Online Contact Form
Document No. 0315-0258
Rev. A
Warranty
Telebyte warrants the equipment to be free from defects
in material and workmanship, under normal and proper use and in its
unmodified condition, for 12 months, starting on the date it is delivered
for use. TELEBYTE's sole obligation under this warranty shall be to
furnish parts and labor for the repair or replacement of products
found by TELEBYTE to be defective in material or workmanship during
the warranty period. Warranty repairs will be performed at the point
of manufacture. Equipment approved for return for warranty service
shall be returned F.O.B. TELEBYTE factory and will be redelivered
by TELEBYTE freight prepaid, except for non- continental U.S.A. locations.
These deliveries will be sent COD freight and import/export charges.
THE ABOVE WARRANTY IS IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED
OR IMPLIED, STATUTORY OR OTHERWISE, INCLUDING ANY IMPLIED WARRANTY
OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. TELEBYTE SHALL
NOT BE LIABLE FOR ANY DAMAGES SUSTAINED BY RESELLER OR ANY OTHER PARTY
ARISING FROM OR RELATING TO ANY EQUIPMENT FAILURE, INCLUDING, BUT
NOT LIMITED TO CONSEQUENTIAL DAMAGES NOR SHALL TELEBYTE HAVE ANY LIABILITY
FOR DELAYS IN REPLACEMENT OR REPAIR OF EQUIPMENT.
Out of warranty equipment may be returned to the Greenlawn, NY customer
service facility prepaid as described above. Return shipping charges
will be billed to the customer. The repaired unit will have a 90 day
warranty. In those cases where "NO TROUBLE" is found, a
reduced charge will be billed to cover handling, testing and packaging.
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