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Fisher-Rosemount RS3 SCI communication protocol

Supported device types and versions
Communication line configuration
Communication station configuration
I/O tag configuration
Literature
Changes and modifications
Document revisions

Supported device types and versions


The protocol supports the data transmission from/to the SCI (Supervisory Computer Interface) interface of the Fisher-Rosemount RS3 control system.

Communication line configuration


For a correct communication of a Rosemount RS3 SCI device, these SCI parameters must be set:

Table 1

Parameter Value
Comm Port Baud Rate 9.2 kbs or 38.4 kbs
Checksum Yes
Data Bits and Parity 8N
XON/XOFF Control Off
EIA Option None
Reply Header String in Hex format 00 00 00 00
Reply Trailer String in Hex format 00 00 00 00
Mode Async Length LSB
Data Format IEEE
TX Gap 100 ms

Communication station configuration


  • Fisher-Rosemount RS3 SCI communication protocol.
  • Address parameters require to define the parameters First index and Update Interval.
    • First index: A value within the interval 0..1499, address of the first I/O tag in the SCI table (Table Entry Location Number).
    • Update interval: Time period for acquisition of new I/O tag values. Possible settings: cont. (continually), 5 sec., 10 sec., 15 sec., 30 sec., 1 min., 2 min., 5 min., 15 min. a 60 min.

SCI allows to configure acquisition of 1500 system values into its table (Table entry) with different parameters (Scaling, Update interval). Table entry are allocated to individual I/O tags from the value First index. The station represents a logic set of tags with the same Update Interval parameter. Update Interval is a time period, using of which SCI acquires new values from the Rosemount S3 system.

Note: As the SCI configuration allows to define the parameter Update Interval up to 300 seconds (5 min.), the settings is used for periods 15 and 60 minutes.


Station protocol parameters

There can be defined the following station protocol parameters:

Table 2

Keyword Full name Meaning Unit Default value
RC Retry Count Poll repetition count in case of a communication error. - 2
RT Retry Timeout Delay between poll repetition in case of a communication error. ms 200
WFT Wait First Timeout Delay after transmitting the poll before reading the response. ms 60
WT Wait Timeout Delay between response readings till its finalization. ms 200
MWR Max Wait Retry Repetition count of response readings till its finalization. - 15
DEBUG Debug Mode If the value of the parameter is YES, the tables on the side of the SCI device are not configured during communication (deletion from tables + initialization of individual points). Parameter is used only for debug purposes. YES/NO NO
SW Send Weak If the value is YES - if there is acquired a new I/O tag value with an error attribute, the error number will be sent to the I/O tag value and the value is marked by the WEAK attribute. It is used for debugging purposes only. YES/NO NO

String containing the protocol parameters is being defined as follows:

Keyword=value;Keyword=value; ...

Example:

SW=YES;WFT=300;

If there is used a keyword with an invalid value in the initialization string, there will be used corresponding default value according the table 2.

I/O tag configuration


Possible I/O tag types: Ai, Ao, Di, Dout

Communication supports value acquisition of I/O tags of the following types:

  • Analog values - I/O tag type AI,AO, used display scaling type “1”
  • Discrete (binary) values - I/O tag type DI, DO, used internal scaling type “0”.

Further it allows to write new values of I/O tags of the following types:

  • Analog values - I/O tag type AO, used display scaling type “1”
  • Discrete (binary) values - I/O tag type DO, used internal scaling type “0”.
Note:

  • Display scaling - acquired values are equal with the RS3 system displaying
  • Internal scaling - discrete values are represented by : 0.0 - log. 0; 1.0 - log. 1

I/O tag address parameters

  • Block Variable - is the name of the Rosemount System 3 block variable. It is being defined in form of e.g. =1E-75 for I/O tag of AI type and e.g. =1F-25/b for I/O tags of DI type.

Literature


  • Rosemount System 3, PeerWay Interfaces Manual, Software Version 18, Release 1, October 1993

Changes and modifications


-

Document revisions


  • Ver. 1.0 – March 5th 2001
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