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RS485 Data Transmission

The RS485 Standard allows a balanced transmission line to be shared in a party-line mode. As many
as 32 driver/receiver pairs can share a two-wire party line network. Many characteristics of the
drivers and receivers are the same as in the RS422 Standard. One difference is that the common
mode voltage limit is extended and is +12V to -7V. Since any driver can be disconnected (or
tri-stated) from the line, it must withstand this common mode voltage range while in the tristate
condition.

The following illustration shows a typical multidrop or party line network. Note that the transmission
line is terminated on both ends of the line but not at drop points in the middle of the line.

Figure A-1:

Typical RS485 Two-Wire Multidrop Network

Page A-3

Manual MRDAG12-8H.Bc2

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Содержание E-RDAG12-8

Страница 1: ...C 10623 Roselle Street San Diego CA 92121 TEL 858 550 9559 FAX 858 550 7322 MODELS RDAG12 8 RDAG12 8H U RDAG12 8 U RDAG12 8H E RDAG12 8 E RDAG12 8H S RDAG12 8 S RDAG12 8H Analog Output Module USER MANUAL FILE MRDAG12 8H Bc2 ...

Страница 2: ...document may contain or reference information and products protected by copyrights or patents and does not convey any license under the patent rights of ACCES nor the rights of others IBM PC PC XT and PC AT are registered trademarks of the International Business Machines Corporation Printed in USA Copyright 2000 by ACCES I O Products Inc 10623 Roselle Street San Diego CA 92121 All rights reserved ...

Страница 3: ...luded by warranty Warranty commences with equipment shipment Following Years Throughout your equipment s lifetime ACCES stands ready to provide on site or in plant service at reasonable rates similar to those of other manufacturers in the industry Equipment Not Manufactured by ACCES Equipment provided but not manufactured by ACCES is warranted and will be repaired according to the terms and condit...

Страница 4: ...d Disk 2 1 Getting Started 2 3 Calibration 2 6 Installation 2 6 Input Output Pin Connections 2 6 Chapter 3 Software 3 1 General 3 1 Command Structure 3 1 Command Functions 3 3 Error Codes 3 10 Appendix A Application Considerations A 1 Introduction A 1 Balanced Differential Signals A 1 RS485 Data Transmission A 3 Appendix B Thermal Considerations B 1 Page iv ...

Страница 5: ... Schematic for Voltage and Current Sink Outputs Page 2 9 Figure A 1 Typical RS485 Two Wire Multidrop Network Page A 3 List of Tables Table 2 1 50 Pin Connector Assignments Page 2 7 Table 3 1 RDAG12 8 Command List Page 3 2 Table A 1 Connections Between Two RS422 Devices Page A 1 Table A 2 RS422 Specification Summary Page A 2 Page v ...

Страница 6: ...y be used to extend the number of Pods on a network Each unit has a unique address Communication uses a master slave protocol wherein the Pod talks only if questioned by the computer An 80C310 Dallas microcontroller with 32k x 8 bits RAM 32K bits non volatile EEPROM and a watchdog timer circuit gives RDAG12 8 the capability and versatility expected from a modern distributed control system RDAG12 8...

Страница 7: ...ffers into the DAC at a programmable rate 31 6 000Hz the units can generate arbitrary waveforms or control signals Model RDAG12 8H is similar except that each DAC output can drive loads up to 250mA using a 12V 2 5A local power supply Digital I O Both models also have seven digital input output ports Each port can be individually programmed as an input or an output Digital input ports can accept lo...

Страница 8: ... Analog Outputs Channels Eight independent Type 12 bit double buffered Non Linearity 0 9 LSB maximum Monotonicity bit Output Range 0 5V 5V 0 10V Output Drive Low Power Option 5 mA High Power Option 250 mA Current Output 4 20 mA SINK User supplied excitation of 5 5V 30V Output Resistance 0 5 Settling Time 15 µsec to LSB Digital I O Seven bits configured as input or output Digital Inputs Logic High ...

Страница 9: ...eat For example when 7 5VDC is applied the temperature rise inside the enclosure is 7 3EC above the ambient temperature Note Maximum operating temperature can be determined according to the following equation I TJ 120 A V 22 5 0 2T A I TJ 120 Where T is the ambient temperature in EC and V is the voltage at which the integral voltage regulator junction temperature will rise to a temperature of 120 ...

Страница 10: ...required voltage drop in long cables is not significant High power version Local Power 12 to 18 VDC at up to 2 A and 12 to 18V at 2A depending on the output load drawn Opto Isolated Section 7 5 to 25 VDC 50 mA Note Due to the small amount of current required voltage drop in long cables is not significant Note If the local power supply has an output voltage greater than 18VDC you can install a Zene...

Страница 11: ...RDAG12 8 Manual Figure 1 1 RDAG12 8 Block Diagram Page 1 6 Manual MRDAG12 8H Bc2 ...

Страница 12: ...Figure 1 2 RDAG12 8 Hole Spacing Diagram Page 1 7 Manual MRDAG12 8H Bc2 ...

Страница 13: ...rd DOS PSAMPLES A subdirectory of CARDNAME that contains Pascal samples DOS CSAMPLES A subdirectory of CARDNAME that contains C samples Win32 language Subdirectories containing samples for Win95 98 and NT WinRISC exe A Windows dumb terminal type communication program designed for RS422 485 operation Used primarily with Remote Data Acquisition Pods and our RS422 485 serial communication product lin...

Страница 14: ...d exe A utility for DOS and Windows to determine what base addresses and IRQs are allocated to installed PCI cards This program runs two versions depending on the operating system Windows 95 98 NT displays a GUI interface and modifies the registry When run from DOS or Windows3 x a text interface is used For information about the format of the registry key consult the card specific samples provided...

Страница 15: ...e through the COM port see details in the appropriate COM card manual View Control Panel Ports NT 4 or Control Panel System Device Manager Ports Properties Resources 9x NT 2000 for information about installed COM ports Communication verification can be done by using a loop back connector with the card in full duplex RS 422 mode A working knowledge of serial ports in Windows will significantly cont...

Страница 16: ...n Option Selection to ensure the jumpers JP2 JP3 and JP4 are in the ISO position 3 Verify your wiring then turn on power to the Pod If you re checking the current draw should be approximately 250mA 4 Now you can again run the setup and calibration program DOS Win3 x 9x This time the setup program should auto detect the Pod from the auto detect menu item and allow you to run the calibration routine...

Страница 17: ...n know that you are communicating effectively with the Pod 3 Connect a DMM set for 20VDC range across pins 1 and 2 of the Pod s screw terminal block Type AC0 0000 00 00 01 0000 and Enter You should receive a CR carriage return from the Pod This command sets Channel 0 for the 0 10V range 4 Now type A0 FFF0 and Enter You should receive a carriage return from the Pod This command causes Channel 0 to ...

Страница 18: ...ecalling these values and adjusting the readings The description of the CALn command shows the order in which the information is stored in the EEPROM Installation The RDAG12 8 and the RDAG12 8H enclosureis anon sealedsteel enclosure with a powder coated finish The enclosure measures 8 long by 5 32 wide by 2 2 high There are three jumper locations on the unit and their functions are as follows JP2 ...

Страница 19: ...33 N A 34 PWR Local Power Supply 35 PWR Local Power Supply 36 PWR Local Power Supply 37 GND Local Power Ground 38 APG5 Analog Power Ground 5 39 VOUT5 Analog Volt Output 5 40 PWR Local Power Supply 41 PBRST Pushbutton Reset 42 ISOGND Isol Power Supply 43 ISOV Isol Power Supply 44 RS485 Communication Port 45 RS485 Communication Port 46 APG6 Analog Power Ground 6 47 VOUT6 Analog Volt Output 6 48 APPL...

Страница 20: ...iode aka flyback diode is required to limit the voltage spike at the output pin when the Relay coil is turned off If different Relay coil voltages are controlled at the Digital outputs then only the highest voltage can be connected to the APPLV pin APG0 7 These terminals are for use with the High Power version of the Pod RDAG12 8H Connect all load returns to these terminals AOGND These terminals a...

Страница 21: ...Figure 2 1 Simplified Schematic for Voltage and Current Sink Outputs Page 2 9 Manual MRDAG12 8H Bc2 ...

Страница 22: ...is considered to be in addressed mode any time its Pod address is not 00 The factory default Pod address is 00 non addressed mode Addressed Mode The address select command must be issued before any other command to the addressed Pod The address command is as follows xx CR where xx is the Pod address from 01 to FF hex and CR is Carriage Return ASCII character 13 The Pod responds with CR Once the ad...

Страница 23: ...ion data for n bbbb mmmm CR CAL BACKUP Restore factory calibration CR Caln xxxx yyyy Write calibration values for channel n CR Command reference for RDAG12 8 H See Desc H Greeting message See Desc V Read firmware revision number n nn CR N Resend Pod s last transmission See Desc POD xx Assign pod to number xx Pod xx CR BAUD nnn Set communication baud rate 1 n 7 Baud 0n CR Mxx Set digital mask to xx...

Страница 24: ... output number 4 to half scale zero volts bipolar or half scale unipolar SEND A4 8000 CR RECEIVE CR Load Buffer for DAC n An iiii xxx0 Writes xxx to DAC n buffer iiii Example Program buffer for DAC 1 to a simple stair step SEND A1 0000 0000 CR RECEIVE CR SEND A1 0001 8000 CR RECEIVE CR SEND A1 0002 FFF0 CR RECEIVE CR SEND A1 0003 8000 CR RECEIVE CR Read Buffer from DAC n An iii Reads from buffer 0...

Страница 25: ... per second SEND S 0399 CR RECEIVE CR Note The sample rate configured is stored in EEPROM on the Pod and will be used as the default power on sample rate The factory default sample rate 100Hz or S 2400 can be restored by sending S 0000 to the Pod Configure Buffers and DACs ACn xxx0 dd tt mm iiii xxx0 is the desired power on initial state of DAC n dd is the divisor for the output rate 00 dd FF tt i...

Страница 26: ...the values required to adjust the measurement readings to agree with the last calibration The setup program will measure and write these calibration parameters The SAMPLE1 program illustrates using the CALn Command with the results of this function Configure Bits as Input or Output Mxx Configures digital bits as inputs or outputs Mx Configures digital bit x as output Mx Configures digital bit x as...

Страница 27: ... write to a bit configured as an input will fail Writing to a byte or word wherein some bits are input and some are output will cause the output latches to change to the new value but the bits which are inputs will not output the value until unless they are placed in output mode Single bit commands will return an error 4 if an attempt is made to write to a bit configured as an input Writing a one ...

Страница 28: ...CR Note The H command returns the version number along with other information See Hello Message following Resend Last Response n Resend last response This command will cause the Pod to return the same thing it just sent This command works for all responses less than 255 characters in length Normally this command is used if the host detected a parity or other line fault while receiving data and nee...

Страница 29: ...Rate Is Set at 9600 BAUD nnn Program the Pod with a new baud rate This command sets the Pod to communicate at a new baud rate The parameter passed nnn is slightly unusual Each n is the same digit from the following table Code Baud Rate 0 1200 1 2400 2 4800 3 9600 4 14400 5 19200 6 28800 7 57600 Therefore valid values for the command s nnn are 000 111 222 333 444 555 666 or 777 The Pod returns a me...

Страница 30: ...ress is not 00 i e the Pod is configured to be in addressed mode it is necessary to issue an address command to the Pod at the new address before it will respond The Pod returns a message containing the Pod number as confirmation Example Set the Pod address to 01 SEND Pod 01 CR RECEIVE Pod 01 CR Set the Pod address to F3 SEND Pod F3 CR RECEIVE Pod F3 CR Take the Pod out of addressed mode SEND Pod ...

Страница 31: ...n some part of the received data contains a parity or framing error Additionally several full text error codes are returned All begin with Error and are useful when using a terminal to program the Pod Error Unrecognized Command command received CR This occurs if the command is not recognized Error Command not fully recognized Command received CR This occurs if the first letter of the command is va...

Страница 32: ... offers all the benefits of RS422 plus allows up to 32 devices to share the same twisted pairs An exception to the foregoing is that multiple RS422 devices can share a single cable if only one will talk and the others will all receive Balanced Differential Signals The reason that RS422 and RS485 devices can drive longer lines with more noise immunity than RS232 devices is that a balanced different...

Страница 33: ...ircuit may operate without the ground connection but may not be reliable Parameter Conditions Min Max Driver Output Voltage unloaded 4V 6V 4V 6V Driver Output Voltage loaded LD and LDGND 2V jumpers in 2V Driver Output Resistance 50Ω Driver Output Short Circuit Current 150 mA Driver Output Rise Time 10 unit interval Receiver Sensitivity 200 mV Receiver Common Mode Voltage Range 7V Receiver Input Re...

Страница 34: ...rence is that the common mode voltage limit is extended and is 12V to 7V Since any driver can be disconnected or tri stated from the line it must withstand this common mode voltage range while in the tristate condition The followingillustration showsatypical multidropor partylinenetwork Notethatthe transmission line is terminated on both ends of the line but not at drop points in the middle of the...

Страница 35: ...RDAG12 8 Manual Page A 4 Manual MRDAG12 8H Bc2 ...

Страница 36: ... voltage Iload Load current Vout Output voltage Thus if the power supply voltage Vs 12v the output voltage range is 0 5V and the load is 40Ohms the power dissipated in the output amplifier by the load current is 7V x 125A 875W The power dissipated by the quiescent current Io 016A Po 24Vx 016A 4w Thus the total power dissipated in the amplifier is 1 275W In the idle mode of operation the outputs no...

Страница 37: ...rature of the heat sink is 125 107 18EC Therefore if any of the channels of the RDAG12 8 has a 250mA load the ambient temperature rise is limited to 18EC The allowable maximum ambient temperature will be 25 18 43EC If forced air cooling is provided then the following calculation will determine the allowable load for the RDAG12 8 allowable power dissipation for the power amplifier amb max max HS JH...

Страница 38: ...accesioproducts com Customer Comments If you experience any problems with this manual or just want to give us some feedback please email us at manuals accesioproducts com Please detail any errors you find and include your mailing address so that we can send you any manual updates ...

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