Omega A2400 manual ?1 BAD Checksum, $1WEF, ?1 Syntax Error

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Command Set 4-4

interprets a command, it looks for the two extra characters and assumes that it is a checksum. If the checksum is not present, the module will perform the command normally. If the two extra characters are present, the module will calculate the checksum for the message. If the calculated checksum does not agree with the transmitted checksum, the module will respond with a ‘BAD CHECKSUM’ error message and the command will be aborted. If the checksums agree, the command will be executed. If the module receives a single extra character, it will respond with a ‘SYNTAX ERROR’ and the command will be aborted. For example:

Command:

$1WE

(no checksum)

Response:

*

 

Command:

#1WEF0

(with checksum)

Response:

*

 

Command:

$1WEF1

(incorrect checksum)

Response:

?1 BAD CHECKSUM

 

Command:

$1WEF

(one extra character)

Response:

?1 SYNTAX ERROR

 

Response Checksums

If the long form ‘#’ version of a command is transmitted to a module, a checksum will be appended to the end of the response. For example:

Command:

$1RD

(short form)

Response:

*+99999.99

 

Command:

#1RD

(long form)

Response:

*1RD+99999.99D9

 

Checksum Calculation

The checksum is calculated by summing the hexadecimal values of all the ASCII characters in the message. The lowest order two hex digits of the sum are used as the checksum. These two digits are then converted to their ASCII character equivalents and appended to the message. This ensures that the checksum is in the form of printable 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