Technical data

Errors during special

function processing

If an error occurs during the processing of the special functions, the

system program reacts in a specific manner.

In terms of the system program reaction to errors, the special

functions can be divided into two groups.

Error OB, ACCU identifiers

Group 1 includes all the special functions for which an error

organization block (error OB) is called in the event of an error. You

can program the CPUs reaction in these error OBs. These error OBs

are OB 19, OB 30 and OB 31. In ACCU 1 and for some special

functions also in ACCU 2 (see Section 5.6.1 and 5.6.2), identifiers are

transferred to the error OB that define the error in greater detail.

If the CPU encounters for example an incorrect parameter when

processing one of these special functions, it detects a runtime error

and calls OB 31. On the other hand, if for example the called special

function does not exist, the CPU detects an operation code error and

attempts to call OB 30. With some of these special functions, if there

is a reference to a data block in the call parameters and the data block

is not loaded, then the CPU attempts to call OB 19.

If the error OBs 30 or 31 are not loaded or contain an STP operation,

the CPU goes into the stop mode. LZF or BCF is marked in the

control bits in the ISTACK. The accumulators of the error processing

levels contain error identifiers that describe the error in greater detail.

If OB 19, OB 30 or OB 31 is loaded (and does not contain an STP

operation), the user program is continued at the next operation after

the OB has been processed. In this case, the accumulators remain

unchanged.

Introduction

CPU 928B Programming Guide

C79000-B8576-C898-01

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