CommandRead input

This edge-triggered input starts the function block operation.

Data type: SAFEBOOL
Initial value: SAFEFALSE

Connection: Connect this input directly or via additional safety-related functions/function blocks as follows:

Either with a safety-related Boolean variable whose value SAFETRUE represents the status "read from recipe file".
Or with a signal from the safety-related application, which represents the request to read a data set from a recipe file.
This can be a signal of a single upstream safety-related function block or the logical connection of signals of several upstream function blocks.
For example, an evaluation of the Safety PLC state could be implemented which triggers the FB to reading a recipe file after starting up the Safety PLC or for setting the safety function into a particular operational state.

Constant SAFETRUE or SAFEFALSE values are not permitted.

If the function block is activated (input Activate = TRUE), the possible values at this input lead to the following function block behavior:

Value Description

SAFETRUE SAFETRUE: Request to read data from the data set. If the command is executed successfully (which includes a successful validation of the read data), Done switches to SAFETRUE.

SAFEFALSE No read operation is requested.

Value	Description
SAFETRUE	SAFETRUE: Request to read data from the data set. If the command is executed successfully (which includes a successful validation of the read data), Done switches to SAFETRUE.
SAFEFALSE	No read operation is requested.

If the recipe file to be read is written by a SF_RecipeWrite FB in the same safety application, the following hazard message must be observed:

WARNING

Non-conformance to safety function requirements

Make sure that the write operation of the SF_RecipeWrite FB is completed successfully prior to reading data from the corresponding recipe file using the SF_RecipeRead FB. For that purpose evaluate the Done output of the SF_RecipeWrite FB and only read values if this output shows the value SAFETRUE.

Be sure that your risk analysis includes an evaluation for the event of using the recipe values although the SF_RecipeWrite FB has not yet indicated its successful completion by setting its Done output to SAFETRUE.