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Addressing

Monitor ASDUs

To determine the address representing the information object in the monitor direction, use the following template:

ASDU_TYPE.IOA.Option[,Read=1], where ASDU_TYPE specifies the type of the represented ASDU (see below), 
IOA specifies the address of the information object, 
Option specifies the attribute represented by the address (see below), 
and the Read=1 (optional) descriptor indicates that the value must be 
requested periodically by sending the command C_RC_NA_1

The Read=1 specifier affects the request procedure if the Enable Reads parameter of the device is set to True.

The table below lists the possible values for ASDU_TYPE.

ASDU_TYPE

ASDU

Description

M_SP

M_SP_NA_1, M_SP_TA_1, M_SP_TB_1

Single-point information.

M_DP

M_DP_NA_1, M_DP_TA_1, M_DP_TB_1

Double-point information.

M_ST

M_ST_NA_1, M_ST_TA_1, M_ST_TB_1

Step position information.

M_BO

M_BO_NA_1, M_BO_TA_1,

M_BO_TB_1

Bit string of 32 bit.

M_ME_NV

M_ME_NA_1, M_ME_TA_1,

M_ME_TD_1

Measured value normalized. This represents a value between -1 and 0.999969482421875.

M_ME_SV

M_ME_NB_1, M_ME_TB_1,

M_ME_TE_1

Measured value scaled. Possible values are -32768 to 32767.

M_ME_FV

M_ME_NC_1, M_ME_TC_1, M_ME_TF_1

Measured value short floating point number.

M_IT

M_IT_NA_1, M_IT_TA_1, M_IT_TB_1

Integrated totals. Read=1 specifier is not supported for this ASDU type.

The table below lists the possible values for Option.

Option

Supported ASDU_TYPE

Description

Value

All types

Represents the value of the information object. If the IV (invalid) bit is set in the quality descriptor of the information object, the tag will go to the Bad state.

COT

All types

Represents the ASDU cause of transmission field.

Quality

All types

Represents the quality descriptor of the information object as a number.

Timestamp

All types

Represents the timestamp CP56Time2a (without any conversion) of the information object. If the information object does not contain a timestamp, the tag will take the value 0001-01-01 00:00:00 and go to the Bad state.

Transient

Only for M_ST

Specifies whether M_ST is in transient state.

SQ

Only for M_IT

Represents the M_IT sequence number.

Note that if the information object contains the timestamp CP56Time2a, it will be used as the timestamp of the tag (taking into account the time zone of the station), otherwise the time ASDU arrival to the server will be used.

It should also be noted that for buffered ASDUs (containing several states of the same information object), the “last” state of the information object will be used as the resulting tag state, but the entire sequence of states will be written to the store (for example, InfluxDB), if such feature is used.

Examples of allowed addresses in the monitor direction:

  •  M_SP.1.COT
  •  M_SP.62.Quality,Read=1
  •  M_SP.40.Timestamp,Read=1
  •  M_SP.1.Value
  •  M_ME_SV.1.Value,Read=1
  •  M_BO.1.Value,Read=1
  •  M_IT.9.Value
  •  M_ME_FV.1.Value

Control ASDUs

To determine the address representing the information object in the control direction, use the following template:

ASDU_TYPE.IOA.Option[.SubOption][.Timestamp], where ASDU_TYPE specifies 
the type 
of the control command (see below), 
IOA defines the address of the information object, 
Option specifies the purpose of the command (see below), 
SubOption (optional) specifies the duration of the command, 
Timestamp (optional) indicates that a timestamp must be sent along 
with the command (the time zone set for the station affects the timestamp generation)

The table below lists the possible values for ASDU_TYPE.

ASDU_TYPE

ASDU

Description

C_SC

C_SC_NA_1, C_SC_TA_1

Single command. Possible values are True or False

C_DC

C_DC_NA_1, C_DC_TA_1

Double command. Possible values are 1 or 2.

C_RC

C_RC_NA_1, C_RC_TA_1

Step command. Possible values are 1 or 2.

C_SE_NV

C_SE_NA_1, C_SE_TA_1

Set point command (normalized value). Possible values are -1 to 0.999969482421875.

C_SE_SV

C_SE_NB_1, C_SE_TB_1

Set point command (scaled value). Possible values are -32768 to 32767.

C_SE_FV

C_SE_NC_1, C_SE_TC_1

Set point command (short value).

C_BO

C_BO_NA_1, C_BO_TA_1

Bit string of 32 bit.

 The table below lists the possible values for Option.

Option

Supported ASDU_TYPE

Description

Execute

All types

Indicates that the control command is executed in one step.

Select

All types except C_BO

The first step of the two-step value writing process known as “select before operation”. The command is executed with the help of sending the Execute command for the same information object.

Deselect

All types except C_BO

Resets the selection command to the initial stage before execution, if a selection has been made for it.

The table below lists the possible values for SubOption.

SubOption

Supported ASDU_TYPE

Description

ShortPulse

C_SC, C_DC, C_RC

The value of the command specifier will be set to 1.

LongPulse

C_SC, C_DC, C_RC

The value of the command specifier will be set to 2.

Persistent

C_SC, C_DC, C_RC

The value of the command specifier will be set to 3.

 Examples of allowed addresses in the control direction:

  •  C_SC.1.Execute
  •  C_DC.15.Select.ShortPulse
  •  C_DC.1.Select.Timestamp
  •  C_SC.73.Select.ShortPulse.Timestamp
  •  C_SC.1.Select.Persistent
  •  C_SC.3219.Deselect.LongPulse
  •  C_SC.1.Deselect.Persistent

Control commands are executed in asynchronous mode. Thus, when writing the value through the OPC UA client, in most cases the result of the writing will be Good. BadNoCommunication is possible if the communication channel is lost or the number of unconfirmed packets is exceeded. After receiving a response ASDU with the cause of transmission ACTIVATION_TERMINATION or DEACTIVATION_CON (depends on the mode: Execute, Select or Deselect), depending on whether the confirmation is positive or negative, the tag will switch to the Good or Bad state, respectively.