Siemens Simatic S7-300 CPU 31xC Series Installation And Operating Instructions Manual page 188

Debugging functions, diagnostics and troubleshooting
10.6 Diagnostics using status and error LEDs
Possible errors
I/O access errors
An error has occurred when
module data was accessed
Global data communication
error, e.g. insufficient length of
the DB for global data
communication.
Tip:
• You can use SFC 39 to disable all interrupts and asynchronous error events.
• You can set the times in the cyclic interrupt OB32 and OB35, starting from 1 ms.
Reference
Details on the OBs and on SFCs required for their evaluation can be found in the
Online Help
Functions
10-12
Note
The shorter the selected cyclic interrupt period, the more likely it is that cyclic interrupt
errors will occur. You must take into account the operating system times of the CPU in
question, the user program runtime and extension of the cycle time by active PG
functions, for example.
and in the Manual
.
Response of the CPU
Calls OB122. CPU does
not STOP if OB122 is
loaded.
Calls OB87. CPU does
not STOP if OB87 is
loaded.
System Software for S7-300/400 - System and Standard
Operating Instructions, Edition 08/2004, A5E00105492-05
Remedies
Check module addressing in HW
Config or whether a module/DP slave
has failed.
Check global data communication in
STEP 7. If required, correct the DB
size.
S7-300, CPU 31xC and CPU 31x: Installation
STEP 7