Omega manual RS-485 Termination, A2400 Operation, Character Filter

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Functional Description 2-4

bus. This bus connects to multidrop RS-485 devices such as D series modules.

8)

(G)DATA- This is the negative polarity of the differential RS-485 bus.

9)

(R)V+

A2400 power connection. The A2400 operates on 10 to 30

volts dc.

 

10) (B)GND

This is the ground connection common to all circuits. The

A2400 does not have isolation between power and the two communications ports.

Note that pins 7 through 10 are designated Y, G, R, and B respectively. This corresponds to the Yellow, Green, Red, and Black colors normally found in common telephone cable. All D series RS-485 devices carry this nomencla- ture. If all yellow connections are connected together, and green to green, etc., the RS-485 wiring will be correct.

RS-485 Termination

The RS-485 port lines are terminated as shown in Fig. 2.1. The 220 ohm resistor is used as a transmission line terminator to improve signal fidelity. A similar 220 ohm resistor should be installed at the far end of the RS-485 bus. The 1 K ohm resistors are used to bias the signal lines to a Mark condition. This is necessary when all transmitters of the RS-485 bus are off, which is the most prevalent condition. The resistor bias helps to prevent noise pickup.

The RS-485 port is protected from potentially destructive voltages with positive temperature coefficient thermistors and transient suppressors.

A2400 Operation

A typical installation is shown in Figure 3.1(see Chapter 3). The A2400 is used to provide an interface between a modem and a string of standard modules. Each module and the A2400 has a unique address. In a typical communications sequence the host computer and radio (not shown) will transmit a module command over the air. The modem receiver picks up the message data and presents it to the A2400 on the RS-232 port.

Character Filter

Due to the nature of radio data transmission, noisy data is almost always present at the output of the modem. This is due to inadequate squelch or noise generated when radio transmitters are turned on and off. The A2400 uses noise reduction techniques to reduce the possibility of bad characters

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Contents User’sGuide For immediate technical or application assistance Servicing North AmericaServicing Europe Omega Engineering ONE Omega Drive Revised 4/17/95BOX STAMFORD, CT Phone 1-800-DAS-IEEETable of Contents Introduction Chapter Getting StartedLeased Lines System Overview+99999.99 $1RDDefault Mode Page Chapter Functional Description Block DiagramFunctional Description Pinout A2400 Operation RS-485 TerminationCharacter Filter Page Programmable Delay Times Page Chapter Communications Command $1RD Response *+99999.99DO, OC, CC, RD, REA, RID, RLP, RS, RSP, RSU Communication DATA+ RS-485 Multidrop SystemPage Command Structure Chapter A2400 Command SetWrite Protection Data StructureMiscellaneous Protocol Notes Response StructureLong Form Responses Command Checksum?1 BAD Checksum ?1 Syntax Error$1WEF A2400 User Commands RT3 A2400 Command SetCommand 01CC Response Response *01CC11 Digital Output do Command DescriptionsCommand $1DO01 Response Command #1DO01 Response *1DO014F Closed Channel CC ExtendedExtended Address EA Command $1DO00 Response Command #1DO00 Response *1DO004E#1ID Tank Farm $1ID Tank Farm1ID Tank Farm 1CD Open Channel OC Extended Command 01OC Response Response *01OCEDRead Data RD Tank Farm $1RID#1RID 1RID Tank Farm 11F#1RSU $1RSU$1RSP #1RSPResponse *1RT1+00100.00DC Read Time Delay 2 RT2 Read Time Delay 1 RT1Response *+00100.00 Page Page Short Prompt SP Error Messages Command 01WE Response *01WE27Address Error BAD ChecksumParity Error Command ErrorSyntax Error Value ErrorCommand Syntax Chapter Setup Information/SetUp Command$1SUbyte 1byte 2byte 3byte Byte HEX Ascii Byte 1 Ascii Printable CharactersBaud Rate ParityCommand $1WE Response Command $1SU31020000 Command $1RS Response *31070000Command $1RS Response *31020102 Command $1WE Bit Command $1RR ResponseByte 2 Linefeed, Parity and Baud Rate BaudNormal addressing Chapter Delay Time Programming Delay Time Programming Page Command $1RT1 Response *+00100.00 Command $1T3+00050.00 Set T3 to 50 ms ResponseChapter Power Supply Symptom RS-232 Module is not responding to commands Chapter TroubleshootingSymptom RS-485 Module is not responding to commands Open/Close Channel Commands Command 01WE ResponseChapter Extended Addressing Typical system overview Command $1RD Response +00100.00 Typical $2RD +00123.45 Command 01OC ResponseCommand 01CC Response Command 02OC ResponseExtended Address Syntax Structured AddressingImplied CC Command OC and CC Command FormatsImplied OC Command Command ResponseCommand 01$1RD Response *+00100.00 Command Response *01OC1D Single Command Module AddressExplicit Open and Close Channel Commands Command 02OC Response 02OC1E ‘1E’ is the checksum Command 01CC Response 01CC11 ‘11’ is the checksumTransparent Mode Functions Chapter Transparent ModeA2400 interfacing a PLC to a leased-line modem A2400 networking several RS-232 devices to a host computer A2400 interfacing a laboratory instrument with modules Transparent Mode Adding secondary control using A2400 modules Transparent Mode WARRANTY/DISCLAIMER Shop online at omega.com