Siemens SIMATIC PCS 7 Function Manual page 6

Overview of the Block Description
Calling OBs
This section contains information about the organization blocks (OBs) in which the block
being described must be installed. When using CFC, the block is installed in the cyclic OBs
(cyclic interrupt) and automatically in the OBs listed in the taskbar of the block (for example,
in OB100 for a hot restart).
During compilation, CFC generates the required OBs. When using the blocks without CFC,
you must program these OBs and call the block instance in them.
Error handling
You can find the error code in the CFC chart at the ENO Boolean block output. The value
corresponds to the BR (binary result in STEP 7 SCL on completion of the block) or the OK
bit (in SCL notation) has the following meaning:
● ENO=BR=OK=1 (TRUE) → The result of the block is correct.
● ENO=BR=OK=0 (FALSE) → The result or the conditions for calculating the result (for
With FBs, you will also find the inverted BR at the output QERR of the instance DB.
● QERR=NOT ENO
The error code is produced in two independent ways:
The operating system detects a processing error (for example, value overflow, called system
functions supply error ID with BR=0). This is a system function and is not described in detail
in the individual block descriptions.
The block algorithm checks whether values and modes are functionally permitted These
errors are documented in the description of the block.
You can evaluate the error code, for example, to create messages or to work with substitute
values instead of incorrect results.
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example, input values, modes) are not valid.
SIMATIC BATCH Interface Blocks V7.1
Function Manual, 03/2009, A5E02171101-01