LGF_StartValueReadWrite (FB / 1.0.0)

Author: Simatic Systems Support

Short description

Read or write start value(s) from variables or complete data blocks

Block Interface


Bool	read	readDone	Bool
Bool	read	readDone	Bool
Bool	write	writeDone	Bool
Bool	write	writeDone	Bool
Variant	dataSource	busy	Bool
Variant	dataSource	busy	Bool
Variant	dataDestination	error	Bool
Variant	dataDestination	error	Bool
		lastRead	DTL
		lastRead	DTL
		lastWrite	DTL
		lastWrite	DTL
		status	Word
		status	Word
		diagnostics	LGF_typeDiagnostics
		diagnostics	LGF_typeDiagnostics

Input parameter

Identifier	Data type	Default value	Description
read	Bool	FALSE	Rising edge: Read start value of data block / Variable of data block
write	Bool	FALSE	Rising edge: Write actual value(s) to start value of data block / Variable of data block
dataSource	Variant	---	Data (block / variable) source, if a separate source is needed. May also be `NULL` - then the target is also used as the source
dataDestination	Variant	---	Data (block / variable) destination

Output parameter

Identifier	Data type	Description
readDone	Bool	TRUE: Read has been completed successfully
writeDone	Bool	TRUE: Write has been completed successfully
busy	Bool	TRUE: FB is not finished and new output values can be expected
error	Bool	TRUE: An error occurred during the execution of the FB
lastRead	DTL	Timestamp of last read access
lastWrite	DTL	Timestamp of last write access
status	Word	16#0000 - 16#7FFF: Status of the FB, 16#8000 - 16#FFFF: Error identification
diagnostics	LGF_typeDiagnostics	Diagnostic information

Status & Error codes

Code / Value	Identifier / Description
16#0001	STATUS_READ_DONE Read execution finished without errors
16#0002	STATUS_WRITE_DONE Write execution finished without errors
16#7000	STATUS_NO_CALL No job being currently processed
16#7001	STATUS_READ Read value(s) in progress
16#7002	STATUS_WRITE Write value(s) in progress
16#8400	ERR_MULTIPLE_COMMANDS Error: Multiple commands add the same time not allowed.
16#8600	ERR_UNDEFINED_STATE Error: Undefined state in state machine
16#8601	ERR_READ Error: Read value(s) `READ_DBL` - see `diagnostics.subfunctionStatus`
16#8602	ERR_WRITE Error: Write value(s) `WRITE_DBL` - see `diagnostics.subfunctionStatus`
16#8611	ERR_READ_TIME Error: Read timestamp `RD_LOC_T` while read values - see `diagnostics.subfunctionStatus`
16#8612	ERR_WRITE_TIME Error: Write timestamp `WR_LOC_T` while write values - see `diagnostics.subfunctionStatus`

User defined datatype(s)

LGF_typeDiagnostics (UDT / V1.0.1)

Diagnostic structure to store and transfer diagnostic information from blocks through the interface.

Identifier	Data type	Default value	Description
status	Word	16#0000	Status of the Block or error identification when error occurred
subfunctionStatus	Word	16#0000	Status or return value of called FB's, FC's and system blocks
stateNumber	DInt	0	State in the state machine of the block where the error occurred

Functional description

The function reads or writes the start value of a single variable, a structured variable or an entire data area or data block from the source to the destination.

The parameter dataDestination must always be present, the parameter dataSource is optional.
If dataSource is not used, the function...

reads the start value(s) of the destination(s) and writes them to the current value of the same variable(s)/data block.
writes the start value(s) of the target to the start value(s) of the same variable(s) of the data block.

NOTE: If the start values are written, the data block then appears in engineering as an "inconsistent" data block after the values have been written by the user program.

NOTE: In order to use complete data blocks, they must be derived from a PLC data type.

Note

A change to the start values can no longer be reversed without further modifications.

The possibilities are, for example:

using an "empty" source with default values
overwriting the value again with a different value
downloading the original data block from the engineering system

Caution: The changes are written to the SMC (Simatic Memory Card).
The SMC is a flash memory with limited write cycles, so you should not write cyclically to the SMC!

Change log

Version & Date		Change description
	1.0.0	Simatic Systems Support
	2025-05-05	First released version