The following section describes the generic MDISDigitalInstrumentObjectType structure and defines the properties associated with it. Additional sections define a subtype MDISDigitalOutObjectType that allows updates to the digital value. This is in general a vendor and operator independent description, but all users of the MDISDigitalInstrumentObjectType or MDISDigitalOutObjectType can add vendor specific data. The vendor specific data should be defined as part of a subtype of the MDISDigitalInstrumentObjectType or MDISDigitalOutObjectType defined in this document. It is assumed that the subsea system is the Server and host of the instance of MDISDigitalInstrumentObjectType or MDISDigitalOutObjectType. The DCS based system is the Client in the system. It is assumed that all interactions with the instance of the MDISDigitalInstrumentObjectType are initiated by the Client and are directed to the Server.

The following section details the MDIS generic properties for the MDISDigitalInstrumentObjectType; implementation shall ensure adherence to Mandatory [M] aspects in order to comply with the MDIS interface standardisation. Optional [O] may or may not be implemented within a project. Figure 12 provides an overview of the MDISDigitalInstrumentObjectType as defined by MDIS, including some nested types. This figure includes all items that are inherited from the MDISBaseObjectType.

Figure 12 - MDISDigitalInstrumentObjectType & MDISDigitalOutObjectType

Table 11 defines the structure of an MDISDigitalInstrumentObjectType. Any vendor specified properties that have been implemented within a project should be documented within a similar format and supplied to the DCS vendor. The addition of vendor specific properties will result in a subtype of the MDISDigitalInstrumentObjectType.

Table 11 - MDISDigitalInstrumentObjectType

Attribute	Value
BrowseName	MDISDigitalInstrumentObjectType
IsAbstract	False
References	Node Class	BrowseName	DataType	TypeDefinition	ModellingRule	RW
Subtype of the MDISBaseObjectType (see section 5.1.1)
HasComponent	Variable	State	Boolean	BaseDataVariableType	Mandatory	R
HasSubtype	MDISDigitalOutObjectType

State – The state of the instance of MDISDigitalInstrumentObjectType. This state is represented as a Boolean, where true indicates on and false indicates off.

Table 12 defines the structure of an MDISDigitalOutObjectType. Any vendor specified properties that have been implemented within a project should be documented within a similar format and supplied to the DCS Vendor. The addition of vendor specific properties will result in a subtype of the MDISDigitalOutObjectType.

Table 12 - MDISDigitalOutObjectType

Attribute	Value
BrowseName	MDISDigitalOutObjectType
IsAbstract	False
References	Node Class	BrowseName	DataType	TypeDefinition	ModellingRule	RW
Subtype of the MDISDigitalInstrumentObjectType
HasComponent	Method	WriteState	See 5.4.5		Mandatory

WriteState – This Method allows a Client to change the value of State on an instance of MDISDigitalOutObjectType. The Method will return any errors that occurred on setting the value. The Client shall verify that the State actually changed to confirm the update.

WriteState Method (defined in Table 13) is used to change the state of the State Variable in an instance of the MDISDigitalOutObjectType. The WriteState operation applies to the object in the subsea system. Some systems will be able to report any errors immediately others will only be able to report that the operation was not refused. Clients are expected to monitor the State and ensure that the operation completed. If an error occurs after the Method has returned, a Fault flag shall be set and an appropriate FaultCode will be returned. The Fault (and FaultCode) will reset on the next successful WriteState Method invocation.

Method Declaration

WriteState (

[in] State Boolean

);

Table 13 – WriteState Method parameters

Argument	Description
State	Boolean indicator of the target state of the variable

Method result codes are defined as part of the Call Service (see OPC UA Services Part 4 – Services specification). They are described in Table 94 for ease of reference.

Comments

The WriteState Method will change the state of the State Variable. The Method will report if any error occurs while writing the state of the Object. Table 14 specifies the AddressSpace representation for the WriteState Method.

Table 14 - WriteState Method AddressSpace Definition

Attribute	Value
BrowseName	State
References		Node Class	BrowseName	DataType	TypeDefinition	Modelling Rule
HasProperty		Variable	InputArguments	Argument[]	PropertyType	Mandatory