Technical data

5.6 Error Information
If an error occurs during system start-up or during cyclic execution of
your program, there are various sources of information to help you
find the problem, as follows:
•• LEDs on the front panel of the CPU
•• ISTACK interrupt stack and control bits
•• system data RS 3, RS 4 and RS 80
•• error identifiers in ACCU 1 and ACCU 2
•• BSTACK block stack
The following sections describe how to evaluate the information
provided by these sources and how to use the error information to
analyze a problem.
LEDs on the Front Panel of
the CPU
If the CPU goes over to the STOP mode when you do not want it to,
check the LEDs on the front panel. They can indicate the cause of the
problem.
LED display Meaning
STOP LED lit continuously The various states of
the STOP LED indicate
specific causes of
interruptions and errors
(see section 4.1).
STOP LED flashes slowly
STOP LED flashes quickly
ADF LED lit continuously Addressing error
QVZ LED lit continuously Timeout error
ZYK LED lit continuously Cycle time exceeded error
5
Error Information
CPU 928B Programming Guide
C79000-B8576-C898-01
5 - 5