Fisher-Rosemount RS3 SCI communication protocol

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

Supported device types and versions

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

Communication line configuration

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

Table 1

Comm Port Baud Rate9.2 kbs or 38.4 kbs
Data Bits and Parity8N
XON/XOFF ControlOff
EIA OptionNone
Reply Header String in Hex format00 00 00 00
Reply Trailer String in Hex format00 00 00 00
ModeAsync Length LSB
Data FormatIEEE
TX Gap100 ms

Communication station configuration

  • Communication protocol: Fisher-Rosemount RS3 SCI.
  • Address parameters require to specify the First index and Update Interval parameters.
    • 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 the acquisition of new I/O tag values. Possible settings: cont. (continuously), 5 sec., 10 sec., 15 sec., 30 sec., 1 min., 2 min., 5 min., 15 min. and 60 min.

SCI allows configuring acquisition of 1500 system values into its table (Table entry) with different parameters (Scaling, Update interval). Table entries are allocated to individual I/O tags starting with the First index value. The station represents a logical set of tags with the same Update Interval parameter. Update Interval is a time period with which the 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.), this setting is used for station polling periods of 15 and 60 minutes.

Station protocol parameters

The following station protocol parameters can be defined:

Table 2

KeywordFull nameMeaningUnitDefault value
Retry CountRequest repetition count in case of a communication error.-2
Retry TimeoutThe delay between request repetitions in case of a communication error.ms200
Wait First TimeoutThe delay after transmitting the request and before reading the response.ms60
Wait TimeoutDelay between response readings until its finalization.ms200
Max Wait RetryRepetition count of response readings until its finalization.-15
Debug ModeIf 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).
The parameter is used only for debugging purposes.
Send WeakIf the value is YES - if a new I/O tag value with an error attribute is acquired, 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/NONO

A string containing the protocol parameters is being defined as follows:

Keyword=value;Keyword=value; ...



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

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”.


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

I/O tag address parameters

  • Block Variable - is the name of the Rosemount System 3 block variable. It is specified in string format, e.g. "=1E-75" (without quotes) for I/O tags of AI type and e.g. "=1F-25/b" for I/O tags of DI type.


  • 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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