PowerLogix COM128 User's Manual
Contents
1. netten ee eran ein Ene dna 8 RS 485 Bus 9 4 3 1 5 unseres 9 4 3 2 General Bus Wiring 9 4 3 3 Recommended Lopologies dd ii 9 SUPPLYING POWER TO THE RS 232 11 TECHNICAL SPECIFICATIONS 13 COM128 OPTIONS ee a aaan 14 BON KS 14 IND Option 14 COM128 Installation and Operation Manual Schneider Electric COM1 28 MULTI PORT RS 232 TO RS 485 CONVERTER FEATURES 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 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 RS 485 to 750 VDC Microprocessor control allows for future enhancements by2. papjaiys 22 OMY 31089 987 89 t dius 1904 987 59 uonosg 989 1015 5984 ty 2 ius Od 58 99190 E p uonoag 995 Joysisay uogeumuja u 4 0007 eJ9AQ paysimy paplelys 9102 98 89 t dius 140d S8p Sy 838g 687 89 1527 10 1819AU0 G8p SH 01 ZEZ SY A9010d01 4001 S8t Su wapo JO 19 01 ZEZ SY 821109 9010401 3NIT LH9IVHIS 987 54 10 128 Installation and Operation Manual CALCULATING OVERALL CABLE LENGTH When determining the overall length of an RS 485 communica tion straight line or loop connection it is important to account for all cable segments For example when RS 485 connections to the device are made via an intermediate terminal block Figure 4 3 2 the lengths of cable between the device and the terminal block must be added to the total cable distance This length is equal to 2 times distance X in the diagram CONNECTION METHODS TO AVOID Any device connection that causes a branch in the main RS 485 bus should be avoided This includes star and tee T methods Refer to Figure 4 3 3b for examples These wiring methods will cause signal refl
3. Send CTS When the COM128 detects that CTS has been asserted it starts to transmit the buffered data out the RS 232 DTE port After the last byte in the buffer has been transmit ted out the RS 232 DTE port the COM128 de asserts the RTS signal and returns to the Idle State If CTS is not asserted after 256 bytes have been received from the RS 485 port a buffer overflow will occur The COM128 de asserts RTS and clears the buffer If CTS is not asserted within 256 byte times after the first byte has been received from the RS 485 port a time out will occur The COM128 de asserts RTS and clears the buffer If CTS is de asserted before the entire contents of the buffer have been transmitted out the RS 232 DTE port the COM128 de asserts RTS and clears the buffer When in the RS 485 to RS 232 Data flow state the COM128 ignores any data received from its RS 232 DTE port Mode Port Baud SW1 sw2 SW3 54 55 56 RTS CTS Flow control DTE 1200 ON OFF OFF OFF OFF OFF RTS CTS Flow control DTE 2400 OFF ON OFF OFF OFF OFF RTS CTS Flow control DTE 4800 ON ON OFF OFF OFF OFF RTS CTS Flow control DTE 9600 OFF OFF ON OFF OFF OFF RTS CTS Flow control DTE 19 200 ON OFF ON OFF OFF OFF COM128 Installation and Operation Manual 3 2 4 RS 485 DATA BUFFERING WITH TRANSMISSION DELAY AFTER RTS ASSERTION APPLICATION This mode is very similar to the RTS CTS mode The COM128 buffers data from the RS 485 ports asserts its RTS output then tr
4. any consequences arising out of the use of this material 70002 0025 06 2006 Schneider Electric All rights reserved 09 2006
5. data Most radio modems require this mode as do some telephone modems Refer to your modem s operation manual to see if your modem provides or requires this handshaking Refer to Section 3 2 Mode Descriptions for examples of switch settings for this application Schneider Electric RS 232 Cable 50 ft max RS 232 Cable 50 ft max Telephone Radio or Fibre Optic Modems e Telephone Network Radio or Fibre Optic Link ern SHLD RS 232 to RS 485 Converter RS 485 Bus RS 485 Cable 22 AWG shielded twisted pair Total length 4000 ft maximum COM128 Installation and Operation Manual 4 3 RS 485 BUS CONNECTIONS 4 3 1 CONVERTOR CONNECTIONS The RS 485 port of the COM128 provides screw down captured wire type terminal blocks that unplug from the main chassis to simplify wiring Refer to the following sections for detailed information on wiring requirements and recommended topologies 4 3 2 GENERAL BUS WIRING CONSIDERATIONS Up to 32 devices can be connected on a single RS 485 bus The overall length of the RS 485 cable connecting all devices cannot exceed 4000 ft 1219 m Devices connected on the bus including convertor s and other instrumentation must be wired as follows a Useagood quality shielded twisted pair cable for each RS 485 bus It is recommended that AWG 22 0 6 mm larger conductor size be used b Ensu
6. firmware upgrade 128 Installation and Operation Manual 1 INTRODUCTION The COM128 is used to interface a single RS 232 communica tions 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 4000 foot 1219 m maximum overall cable length on RS 485 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 RS 485 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
7. o ZE2 SH X gt 8cLINOO u N quus 1909 989 59 1909 981 59 1 98 59 NOILOANNOO L S8t SH mus YOd x 4 B JO LOANNOD EAS JON quus T HOd T HOd ABUSAUND 98 5 01 CEC SH 8cLNOO jou 5 MHS em e Beau Bes 12 COM128 Installation and Operation Manual 6 TECHNICAL SPECIFICATIONS ELECTRICAL RATINGS Isolation 750 V between RS 232 and RS 485 ports Power Supply Standard 9 VDC 500 mA 120 VAC adapter supplied Alternate 2 pin pluggable terminal block accepts 9 30 VDC Power to DTR Pin 5 VDC Q 10 mA jumper selectable Operating Temperature 0 C TO 50 C 32 F to 122 F ambient air Storage Temperature 30 C to 70 C 22 F to 158 F Humidity 5 to 95 percent non condensing Shipping Weight 0 9 kg 2 108 0 02 Carton 30 x 25 x 18cm 11 8 x 9 8 x 5 9 FEATURES Schneider Electric Baud Rates Supported 1200 2400 4800 9600 19200 RS 232 Ports RS 485 Ports One DTE Male DB9 One DCE Male 089 Four 3 pin pluggable terminal blocks each with and shield SHLD terminals RS 485 port terminals all pass ANSI IEEE C37 90A 1989 surge withstand and fast transient tests Figure 6 1 COM128 Mechanical Dimensions 2 13 54 rubber feet 5 25 133mm COM128 Installation and O
8. signal reflections which may corrupt data on the bus Termination resistors are connected between the and terminals of the device at each end of the bus This device can include either a convertor or any other instrument The value of the resistor should match the line impedance of the cable being used For AWG 22 shielded twisted pair cable values between 150 and 300 ohms are typical Consult the cable manufacturer s documentation for the exact impedance of your cable LOOP TOPOLOGY The loop wiring method is illustrated in Figure 4 3 3a The COM128 can exist at any position on the RS 485 bus One advantage of the loop topology is that a single open circuit fault condition anywhere on the loop will not result in the loss of communication between the computer station and any of the remote devices The loop topology does not require termination resistors at any point on the bus RS 485 Terminal RS 485 Cable Device Sirip 22 gauge shielded e twisted pair RS 485 PORT SHLD NOTE 2 0 To next 2 NEM device Terminal strip connection method adds 2 times distance X to overall RS 485 cm cable length er a 111 DISTANCE X Schneider Electric COM128 Installation and Operation Manual THS 4 0007 121340 1908 S8p Sy ped
9. the RS 485 buses When the RTS signal is de asserted the COM128 will listen for data on the RS 485 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 Schneider Electric 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 5 232 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 secti
10. Buffering with 20 mSe c transmission delay after RTS assertion 1200 OFF OFF OFF OFF OFF ON RS 485 Data Buffering with 50 mSec transmission delay after RTS assertion DTE 1200 ON OFF OFF OFF OFF ON RS 485 Data Buffering with 100 mSec transmission delay after RTS assertion DTE 1200 OFF ON OFF OFF OFF ON RS 485 Data Buffering with 20 mSec transmission delay after RTS assertion DTE 2400 ON ON OFF OFF OFF ON RS 485 Data Buffering with 50 mSec transmission delay after RTS assertion DTE 2400 OFF OFF ON OFF OFF ON RS 485 Data Buffering with 100 mSec transmission delay after RTS assertion 2400 ON OFF ON OFF OFF ON RS 485 Data Buffering with 20 mSec transmission delay after RTS assertion DTE 4800 OFF ON ON OFF OFF ON RS 485 Data Buffering with 50 mSec transmission delay after RTS assertion DTE 4800 ON ON ON OFF OFF ON RS 485 Data Buffering with 100 mSec transmission delay after RTS assertion 4800 OFF OFF OFF ON OFF ON RS 485 Data Buffering with 20 mSec transmission delay after RTS assertion DTE 9600 ON OFF OFF ON OFF ON RS 485 Data Buffering with 50 mSec transmission delay after RTS assertion DTE 9600 OFF ON OFF ON OFF ON RS 485 Data Buffering with 100 mSec transmission delay after RTS assertion 0600 ON ON OFF ON OFF ON RS 485 Data Buffering with 20 mSec transmission delay after RTS assertion DTE 19 200 OFF OFF ON ON OFF ON RS 485 Data Buffering with 50 mSec transmission delay after RTS assertion DTE 19 200 ON OFF ON ON OFF ON RS 485 Data Buffer
11. F RS 485 Flow Control fixed Baud Rate DTE 9600 ON ON OFF OFF ON OFF RS 485 Flow Control fixed Baud Rate DTE 19 200 OFF OFF ON 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 ON OFF ON ON OFF RS 485 Flow Control with Auto Baud Rate Detect DTE NA ON ON OFF ON ON OFF RS 485 Flow Control with Auto Baud Rate Detect and Carrier Detect Required DTE NA OFF OFF ON ON ON OFF RS 485 Flow Control with Hardware RTS DCE NA ON OFF ON ON ON OFF COM128 Installation and Operation Manual Schneider Electric 3 2 2 SPEED COMPENSATION APPLICATION For use with DCE devices that require very accurate baud rate input Typical uses are with high speed dial up modems This mode can be programmed to either ignore the Carrier Detect CD input of its RS 232 DTE port or require that CD be asserted by the DCE device before data is transmitted by the COM128 to the DCE device Mode Port Baud swi sw2 SW3 sw4 SW5 SW6 Speed Compensation w o Carrier Detect DTE 1200 OFF ON ON OFF OFF OFF Speed Compensation w o Carrier Detect DTE 2400 ON ON ON OFF OFF OFF Speed Compensation w o Carrier Detec
12. PowerLogic COM128 RS 232 to RS 485 Converter Installation and Operation Guide August 2006 Conventions Throughout this operation manual the following methods are used to highlight important information NOTE Describes important considerations related to a device setup feature or application CAUTION Alerts you to a condition which could potentially cause damage to the device or other external equipment WARNING or DANGER Warns you to avoid conditions that could potentially cause serious personal injury and or equipment damage 2 1 2 2 3 1 3 2 4 1 4 2 4 3 7 1 7 2 Table of Contents COM128 FEATURES 1 INTRODUCTION eu 2 Physical Features e 3 5 232 c 3 85 485 A HERE Cree HERR ae een 3 CONFIGURATION 4 Configuration Switches do a 4 Mode 0 asia ls 4 3 2 1 5 485 Flow Control ee eine 4 3 2 2 Speed 5 3 2 3 ATS CTS Control een 3 2 4 RS 485 Data 6 3 2 5 aem 6 INSTALLATION ici ii a 7 Supply Connections la iii orante 7 RS 232 Connection 8 Configuration 7 4 2 1 RS 282 Cable ide 7 4 2 2 Direct Connection to a Computer 7 4 2 3 Connectionito
13. ansmits data out of the DTE port after a programmable time delay This mode is used in conjunction with DCE devices which require hardware flow control handshaking but do not provide a CTS signal back to the COM128 Typical uses are radio modems and multi drop lease line modems with switched carriers RS 232 TO RS 485 DATA FLOW The COM128 detects the start bit or falling edge of the first byte received by the RS 232 DTE port and sets all 4 RS 485 ports into Transmit mode The COM128 continues to Schneider Electric monitor the RS 232 DTE port for data and continues to pass data to the RS 485 port until there is no data coming into the RS 232 port RS 485 TO RS 232 DATA FLOW The COM128 detects data received on any of the 4 RS 485 ports The first byte is stored in an internal memory buffer and the Request To Send RTS output signal of the DTE RS 232 port is asserted and an internal timer is started The buffer size is 256 bytes The COM128 continues to buffer bytes received from the RS 485 port When the COM128 s internal timer has elapsed it starts to transmit the buffered data out the RS 232 DTE port After the last byte in the buffer has been transmitted out the RS 232 DTE port the COM128 de asserts the RTS signal and returns to the Idle State When in the RS 485 to RS 232 Data flow state the COM128 ignores any data received from its RS 232 port Mode Port Baud SW1 SW2 SW3 SW4 SW5 SW6 RS 485 Data
14. ections that may cause interference RULE OF THUMB At any connection point on the RS 485 bus no more than two 2 cables should be con nected This includes connection points on instruments converters and terminal strips Following this guideline ensures that star and tee connections are avoided 5 SUPPLYING POWER TO THE RS 232 DTR PIN The 128 is shipped configured for use with devices that supply their own power Some RS 232 devices such as short haul modems and line drivers receive their power from the DTR pin of the RS 232 line The 128 can be configured to support these devices supplying 5 VDC 10 mA to the DTR pin of its DTE or DCE port To configure the COM128 to supply power on the DTR pin follow this procedure 1 Disconnect all power and communications connections to the COM128 2 Remove the two case screws and lift the top half of the case away from the base of the unit 3 Locate the 3 pin jumper blocks J1 and J2 For normal use these are configured with pins 2 and 3 connected Change each jumper so that pins 1 and 2 are connected 4 Replace the cover and re install the screws Schneider Electric Schneider Electric COM128 Installation and Operation Manual LOANNOO LON 09 Jo Jeinduio2 CS auionuo5
15. ere otherwise indicated Connections The IND power supply must be connected to a dedicated fused feed voltage source The COM128 is connected to the IND supply via the Phoenix 2 pin power supply connector on the COM128 enclosure Refer to Figure 7 2 128 Installation and Operation Manual COM128 see specs for gt for input range gt 1A Slo Blo Bx AC L AC N IND Power Supply Schneider Electric COM128 Installation and Operation Manual Schneider Electric 3 832 TY sel ime CO o LO Y O EU Zz DIMEN 16 PowerLogic 128 Installation and Operation Manual For further assistance please contact us at Schneider Electric Power Monitoring and Control 2195 Keating Cross Road Saanichton BC Canada V8M 2A5 Tel 1 250 652 7100 295 Tech Park Drive Suite 100 Lavergne TN 37086 USA Tel 1 615 287 3400 Electropole 38 EQI 31 rue Pierre Mend s France F 38050 Grenoble C dex 9 Tel 33 0 4 76 57 60 60 Getting technical support Contact your local Schneider Electric sales representative for assistance or go to the www powerlogic com website Electrical equipment should be installed operated serviced and maintained only by qualified personnel No responsibility is assumed by Schneider Electric for
16. ing with 100 mSec transmission delay after RTS assertion DTE 19 200 OFF ON ON ON OFF ON 3 2 5 REPEATER Mode Port Baud SWi SW2 SW3 SW4 595 546 se D do not share data The 5 232 ports are not Repeater NA 4800 ON OFF ON OFF ON ON used That is port A can transmit to B C and D and ports Repeater NA 9600 OFF ON OFF ON ON BorC or D can transmit to A 128 Installation and Operation Manual 4 INSTALLATION 4 1 DC SUPPLY CONNECTIONS The COM128 is shipped with 9 VDC adapter which plugs into the adapter receptacle Use only the adapter provided with the COM128 for this particular powering application Alternatively DC power supply capable of supplying from 9 to 30 VDC at 500 mA minimum can be used to power the COM128 Connect the and outputs from the power supply to the corresponding terminals of the removable 2 pin terminal block connector supplied with the COM128 See Chapter 2 Figure 2 1 1 4 2 RS 232 CONNECTIONS amp CONFIGURATION Sections 4 2 2 and 4 2 3 discuss RS 232 port connections when connecting to a computer or modem The COM128 configuration switches are used to select which port is active Note that the 128 can also be used in other applications by selecting the appropriate port and modes as described in Chapter 3 For configuration switch settings refer to section 32 Mode Descriptions 4 2 1 RS 232 CABLE A standard RS 232 serial communication
17. ollows each mode description The configuration switches are only read when control power is initally applied to the COM128 re configure the COM128 the control power must be removed and re applied OFF 3 2 MODE DESCRIPTIONS 3 2 1 RS 485 FLOW CONTROL Setting the Configuration Switches to an FUNCTION undefined value will cause the COM128 to This mode is used to convert the RS 232 signals from either a continually reset DTE DCE device to 5 485 signals The COM128 makes the signal conversion and provides the timing control signals for the 5 485 ports No data buffering takes place Timing can be set for a fixed baud rate the COM128 is able to do auto matic baud rate detection on the incoming 5 232 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 5 232 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 Mode Port Baud SW1 SW2 SW3 SW4 SW5 SW6 RS 485 Flow Control fixed Baud Rate DTE 1200 OFF OFF OFF OFF ON OFF RS 485 Flow Control fixed Baud Rate DTE 2400 ON OFF OFF OFF ON OFF RS 485 Flow Control fixed Baud Rate DTE 4800 OFF ON OFF OFF ON OF
18. ons 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 replace ment 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 COM128 Installation and Operation Manual 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 modem See Chapter 3 for configuration See Chapter 4 for connections SWITCH The 6
19. peration Manual 7 COM128 OPTIONS UNI OPTION The UNI option is a universal power supply that allows the COM128 to be powered from any standard international voltage and frequency Specifications Input Voltage 90 VAC to 264 VAC Input Frequency Range 47 Hz to 63 Hz Protection Internal Fuse Operating Temperature 0 C to 40 C 32 F to 104 F Storage Temperature 40 C to 70 C 40 F to 158 F Standards Compliance The UNI option is CSA and UL approved and CE compliant Schneider Electric IND OPTION The IND option is a universal power supply that allows the COM128 to be powered from any standard international voltage and frequency The power supply is designed for industrial applications where it can be mounted on the wall or door of a cabinet Refer to Figure 7 2 1 Specifications Input Voltage 85 VAC to 264 VAC 110 VDC to 340 VDC InputFrequencyRange 47 Hz 440 Hz Protection Internal fuse Operating Temperature 0 C to 50 C relative humidity non condensing 32 F to 122 F Storage Temperature 20 C to 75 C 4 F to 167 F STANDARDS COMPLIANCE The IND option is CSA UL and VDE approved and CE certified SPECIAL CONSIDERATION For the CE certification to be valid the IND power supply must be installed in accor dance with all local electrical codes and standards and must not be user accessible during normal operation Mechanical and Mounting Dimensions Dimensions in inches except wh
20. position switch is used to configure the operation of the COM128 See Chapter 3 for additional details Figure 2 1 1 SUPPLY Schneider Electric 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 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 RS 232 port C RS 485 OUT A C D For each corresponding 5 485 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 RS 232 Connection Panel Figure 2 2 1 STATUS RS 485 PORTS RS 485 Connection Pane 128 Installation and Operation Manual Schneider Electric 3 CONFIGURATION 3 1 CONFIGURATION SWITCHES SWITCHES These six switches are used to configure the COM128 for the desired operation see Figure 3 1 1 switch is ON when it is in the UP position The following is description of each mode of operation A list of switch settings for the different modes ON 2 f
21. re that the polarity is correct when connecting to the RS 485 port and terminals of each device c The shield of each segment of the RS 485 cable must be connected to ground at one end only Do not connect ground to the shield at both ends of asegment Doing so will allow ground loop currents to flow in the shield inducing noise in the communications cable d It is recommended that an intermediate terminal strip be used to connect each device to the bus This will allow for easy removal of a device for servicing if necessary The terminal strip should be connected as shown in Figure 4 3 2 Schneider Electric 4 3 3 RECOMMENDED TOPOLOGIES Devices on an RS 485 bus are connected in a point to point configuration with the and terminals of each device connected to the associated terminals on the next device This is illustrated in Figure 4 3 3a While there are many topologies that can be used to connect devices on an RS 485 communication bus the two recom mended methods are the straight line and loop topologies STRAIGHT LINE TOPOLOGY The straight line wiring method is illustrated in Figure 4 3 3a Note that connections are shown for one RS 485 port only The COM128 supports four RS 485 buses simultaneously The COM 128 can exist at any position on RS 485 bus including an end point Each end point of the straight line bus must be terminated with a 1 4 watt resistor These termination resistors reduce
22. s cable should be used The COM128 end must be a female DB9 connector for direct connection or a male DB25 for connection via the supplied adapter plug Maximum cable length is 50 feet 15 2 m Schneider Electric 4 2 2 DIRECT CONNECTION TO ACOMPUTER PORT SELECTION An IBM compatible PC acts as a Data Terminal Equipment RS 232 device Therefore the computer s RS 232 port should be connected to the DCE port on the COM128 Refer to Figure 4 2 2 SWITCH SETTINGS To properly communicate with the computer the COM128 must be configured as a DCE Data Communications Equipment RS 232 device see subsection 3 2 1 RS 485 Flow Control RS 232 Cable 50 ft max To RS 485 Bus RS 485 Cable AWG 22 shielded twisted pair Total length 4000 ft maximum COM128 RS 232 to RS 485 Converter COM128 Installation and Operation Manual 4 2 3 CONNECTION TO AMODEM PORT SELECTION A telephone or radio modem typically acts as DCE RS 232 device Therefore the modem s RS 232 port should be connected to the COM128 s DTE RS 232 port Refer to Figure 4 2 3 SWITCH SETTINGS To properly communicate with the modem the COM128 must be configured as a DTE RS 232 device If the modem requires RTS CTS handshaking the RTS CTS Flow Control function provided by the COM128 should be enabled This will force the COM128 to buffer all RS 485 data received until the modem is ready to receive the
23. t DTE 4800 OFF OFF OFF ON OFF OFF Speed Compensation w o Carrier Detect DTE 9600 ON OFF OFF ON OFF OFF Speed Compensation w o Carrier Detect DTE 19 200 OFF ON OFF ON OFF OFF Speed Compensation with Carrier Detect DTE 1200 ON ON OFF ON OFF OFF Speed Compensation with Carrier Detect DTE 2400 OFF OFF ON ON OFF OFF Speed Compensation with Carrier Detect DTE 4800 ON OFF ON ON OFF OFF Speed Compensation with Carrier Detect DTE 9600 OFF ON ON ON OFF OFF Speed Compensation with Carrier Detect DTE 19 200 ON ON ON OFF OFF 3 2 3 RTS CTS FLOW CONTROL APPLICATION This mode is used in conjunction with DCE devices which require hardware RTS CTS handshaking Typical uses are radio modems and multi drop lease line modems with switched carriers RS 232 TO RS 485 DATA FLOW The COM128 detects the start bit or falling edge of the first byte received by the RS 232 DTE port and sets all 4 RS 485 ports into Transmit mode The COM128 continues to monitor the RS 232 DTE port for data and continues to pass data to the RS 485 port until there is no data coming in the RS 232 port RS 485 TO RS 232 DATA FLOW The COM128 detects data received on any of the 4 RS 485 ports The first byte is stored in an internal memory buffer and the Request To Send RTS output signal of the DTE RS 232 port is asserted The buffer size is 256 bytes The COM128 continues to buffer bytes received from the RS 485 port and scans the RS 232 ports input signal Clear
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