PowerLogix COM128 User Manual
PowerLogic® COM128
RS-232 to RS-485 Converter
Installation and Operation Guide
August 2006
Conventions
Throughoutthisoperationmanual,thefollowingmethodsareusedtohighlight
importantinformation.
NOTE
Describesimportantconsiderationsrelatedtoadevicesetup,featureor
application.
CAUTION
Alertsyoutoaconditionwhichcouldpotentiallycausedamagetothedeviceor
otherexternalequipment.
WARNING or DANGER
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and/orequipmentdamage.
personalinjury
Table of Contents
COM128 FEATURES ................................................................................................. 1
1 INTRODUCTION ........................................................................................................ 2
2 Physical Features ..................................................................................................... 3
2.1 RS-232 Panel ............................................................................................................. 3
2.2 RS-485 Panel ............................................................................................................. 3
3 CONFIGURATION ...................................................................................................... 4
3.1 Configuration Switches ............................................................................................... 4
3.2 Mode Descriptions ...................................................................................................... 4
3.2.1 RS-485 Flow Control ................................................................................... 4
3.2.2 Speed Compensation ................................................................................. 5
3.2.3 RTS / CTS Flow Control ............................................................................. 5
3.2.4 RS-485 Data Buffering ................................................................................ 6
3.2.5 Repeater ..................................................................................................... 6
4 INSTALLATION ......................................................................................................... 7
4.1 DC Supply Connections.............................................................................................. 7
4.2 RS-232 Connection & Configuration ........................................................................... 7
4.2.1 RS-232 Cable ............................................................................................. 7
4.2.2 Direct Connection to a Computer ................................................................7
4.2.3 Connection to a Modem .............................................................................. 8
4.3 RS-485 Bus Connections ........................................................................................... 9
4.3.1 Convertor Connections ............................................................................... 9
4.3.2 General Bus Wiring Considerations ............................................................ 9
4.3.3 Recommended Topologies ......................................................................... 9
5 SUPPLYING POWER TO THE RS-232 DTR PIN .................................................... 11
6 TECHNICAL SPECIFICATIONS .............................................................................. 13
7 COM128 OPTIONS .................................................................................................. 14
7.1 -UNI Option .............................................................................................................. 14
7.2 -IND Option .............................................................................................................. 14
COM128 Installation and Operation Manual Schneider Electric
TM
COM128
MULTI-PORT RS-232 TO RS-485 CONVERTER
•
Connects one RS-232 line to four RS-485 buses.
•
Automatic baud rate detection supporting data
rates of 1200, 2400, 4800, 9600, and 19200 baud.
• DTE or DCE operation allows connection to
computers or modems without the need for null
modem adapters.
• RS-485 transmit enable may be controlled
automatically, or by the RS-232 RTS line.
• RTS/CTS handshaking capability for use with radio
modems.
FEA TURES
• Compatible with short-haul modems and line
drivers that are powered by the RS-232 line.
• Works directly with M-SCADA, L-SCADA
and PowerView software, or with other
proprietary software.
• Full electrical isolation between RS-232 and RS485 to 750 VDC
• Microprocessor control allows for future
enhancements by firmware upgrade.
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COM128 Installation and Operation Manual Schneider Electric
1 INTRODUCTION
The COM128 is used to interface a single RS-232 communications line to up to four RS-485 communications buses.
The RS-485 standard restricts each RS-485 bus to supporting
32 or fewer devices connected to it. The standard also dictates
a 4000 foot (1219 m) maximum overall cable length on an RS485 bus. The COM128 is ideal for installations that contain
more than 32 remote devices, or that have devices positioned at
distances greater than could be reached with a 4000 foot cable.
The COM128 has four physically independent RS-485 ports,
allowing communications with up to 128 devices. Data is
transmitted to all four RS-485 ports simultaneously (ie. the
ports are not addressable).
The COM128 provides many features which make it flexible,
easy to use, and reliable:
TWO METHODS OF RS-485 BUS CONTROL
RS-232 is a duplex communications standard, allowing signals
to be transmitted and received simultaneously. RS-485 is half
duplex standard, allowing only one device connected to an RS485 bus to transmit at any given time.
The COM128 has two ways to determine whether it should be
transmitting onto the RS-485 buses, or listening to them:
1) The COM128 can use the RTS signal generated by a
computer or other device connected to the RS-232 port.
When the RTS line is asserted, the COM128 will convert
the RS-232 data stream to RS-485 signal levels and
transmit onto the RS-485 buses. When the RTS signal is
de-asserted, the COM128 will listen for data on the RS485 bus and pass it through to the RS-232 port.
2) Some types of modems and computer hardware/software
do not support RTS line operation. For these applications,
the COM128 has an Auto RTS mode which monitors the
RS-232 bus for data signals. When data is present, the
COM128 automatically enables the RS-485 transmit mode
and begins to transmit onto the RS-485 buses.
DTE OR DCE OPERATION
The COM128 is switch-selectable to act in DTE or
DCE mode. An RS-232 port is provided for each mode,
eliminating the need for null-modems.
In DTE mode, the COM128 supports a CTS-WAIT mode in
which received RS-485 packets will be buffered until the CTS
line indicates the RS-232 device is ready to receive the data.
This feature is useful when interfacing radio modems or slow
data logging equipment to RS-485 devices.
AUTOMATIC BAUD RATE DETECTION
The microprocessor within the COM128 continuously monitors
the data being received on its RS-232 port, and determines the
correct baud rate. No jumper or switch settings are required.
HIGH ELECTRICAL ISOLATION
RS-485 buses are generally quite long, and are often run
through electrically noisy environments. The risk of exposure to
transient voltage surges and spikes on an RS-485 line is
substantially higher than on an RS-232 line. The COM128 uses
optical isolation between RS-485 and RS-232 sections to
provide 750 VDC electrical isolation, and includes transient
suppression circuitry on its RS-485 ports.
MICROPROCESSOR CONTROL
Unlike most converters, the COM128 is controlled by a
microprocessor. COM128 features are determined by the
processor, not by its electrical circuitry. As new features
become available, they can be added to the COM128 by a
simple firmware upgrade. This process requires the replacement of a single chip, allowing upgrades to be performed in the
field in a matter of minutes.
LINE DRIVER COMPATIBILITY
Short-haul modem/line drivers, such as the Gandalf mLDS,
draw their power from the RS-232 DTR line. The COM128 will
support these devices by means of a simple process that
requires the movement of a jumper within the COM128 case.
The process requires only a screwdriver and should take no
more than a few minutes to perform. Please refer to Chapter 5
(Page 12) "Supplying Power to the RS-232 DTR Pin" for details.
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COM128 Installation and Operation Manual Schneider Electric
2 PHYSICAL FEATURES
2.1 RS-232 PANEL
The RS-232 panel of the COM128 is illustrated in Figure 2.1.1.
DC SUPPLY CONNECTORS
These connections allow the COM128 to be powered from a
wide range of DC voltage sources, including the supplied
adapter. See Chapter 4 for additional information.
RS-232 PORTS
These ports provide connection to either a computer (DCE) or
a modem (DTE) See Chapter 3 for configuration. See
Chapter 4 for connections.
SWITCH
The 6-position switch is used to configure the operation of the
COM128. See Chapter 3 for additional details.
2.2 RS-485 PANEL
The RS-485 panel of the COM128 is illustrated in Figure 2.2.1.
RS-485 PORTS
These four ports connect the COM128 to the four
RS-485 buses. Four pluggable 3-pin terminal blocks are
provided.
STATUS INDICATORS
A. IN (RS-232)
This LED will flash to indicate that data is being passed
from the connected RS-232 port to the RS-485 ports.
B. IN (RS-485)
This LED will flash to indicate that data is being passed
from one of the four RS-485 ports to the connected RS232 port.
C. RS-485 OUT (A, B, C, D)
For each corresponding RS-485 port these LED’s indicate
if the port is in receive or transmit mode. If the LED is
on, the corresponding port is listening for data from the
RS-485 bus. If the LED is off, the corresponding port is
transmitting data to the RS-485 bus.
Figure 2.1.1 RS-232 Connection Panel
Figure 2.2.1 RS-485 Connection Panel
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COM128 Installation and Operation Manual Schneider Electric
3 CONFIGURATION
3.1 CONFIGURATION SWITCHES
These six switches are used to configure the COM128 for the
desired operation (see Figure 3.1.1). A switch is ON when it is
in the UP position. The following is a description of each mode
of operation. A list of switch settings for the different modes
follows each mode description. The configuration switches are
only read when control power is initally applied to the
COM128. To re-configure the COM128, the control power
must be removed and re-applied.
3.2 MODE DESCRIPTIONS
3.2.1 RS-485 FLOW CONTROL
FUNCTION
This mode is used to convert the RS-232 signals from either a
DTE or DCE device to RS-485 signals. The COM128 makes the
signal conversion and provides the timing control signals for
the RS-485 ports. No data buffering takes place. Timing can be
set for a fixed baud rate or the COM128 is able to do automatic baud rate detection on the incoming RS-232 data. Either
the DTE or DCE port can be programmed. When the DTE port
of the COM128 is selected in automatic baud rate detection
mode, the input CD (Carrier Detect) signal from the DCE
device can be used to control the transmission of RS-232 data
from the COM128 to the DCE device.
For applications where a DTE device uses the RS-232 RTS
signal for flow control the COM128 can be programmed to use
the RTS signal to control the RS-485 ports.
Figure 3.1.1 COM128 Configuration Switches
SWITCHES
SW2
SW1
ON
1 2 3 4 5 6
OFF
Setting the Configuration Switches to an
undefined value will cause the COM128 to
continually reset.
SW3
NOTE
SW4
SW5
SW6
Mode Port Baud SW1 SW2 SW3 SW4 SW5 SW6
RS-485 Flow Control @ fixed Baud Rate DT E 1200 OFF OFF OFF OFF ON OFF
RS-485 Flow Control @ fixed Baud Rate DT E 2400 ON OFF OFF OFF ON OFF
RS-485 Flow Control @ fixed Baud Rate DT E 4800 OFF ON OFF OFF ON OFF
RS-485 Flow Control @ fixed Baud Rate DT E 9600 ON ON OFF OFF ON OFF
RS-485 Flow Control @ fixed Baud Rate DT E 19,200 OFF OFF O N OFF ON OFF
RS-485 Flow Control @ fixed Baud Rate DCE 1200 ON OFF ON OFF ON OFF
RS-485 Flow Control @ fixed Baud Rate DCE 2400 OFF ON ON OFF ON OFF
RS-485 Flow Control @ fixed Baud Rate DCE 4800 ON ON ON OFF ON OFF
RS-485 Flow Control @ fixed Baud Rate DCE 9600 OFF OFF OFF ON ON OFF
RS-485 Flow Control @ fixed Baud Rate DCE 19,200 ON OFF OFF ON ON OFF
RS-485 Flow Control with Auto Baud Rate Detect DCE NA OFF O N OFF O N ON OFF
RS-485 Flow Control with Auto Baud Rate Detect DT E N A ON O N OFF O N ON OFF
RS-485 Flow Control with Auto Baud Rate Detect and Carrier Detect Required DT E N A OFF OFF ON O N O N OFF
RS-485 Flow Control with Hardware RTS DCE NA O N OFF O N O N ON OFF
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