Technical data

Table Of Contents
Organization Blocks
System Software for S7-300/400 System and Standard Functions - Volume 1/2
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A5E00709327-01
1.28 I/O Access Error Organization Block (OB122)
Description
The operating system of the CPU calls OB122 whenever an error occurs while
accessing data on a module. For example, if the CPU detects a read error when
accessing data on an I/O module, the operating system calls OB122.
Understanding the Operation of the I/O Access Error OB
OB122 is executed in the same priority class as the interrupted OB. If OB122 is not
programmed, the CPU changes from the RUN mode to the STOP mode.
S7 provides the following SFCs for masking and unmasking start events for OB122
during the execution of your program:
SFC36 (MSK_FLT): masks specific error codes
SFC37 (DMSK_FLT): unmasks the error codes that were masked by SFC36
SFC38 (READ_ERR): reads the error register