Siemens SIMATIC S7-300 Hardware And Installation Manual page 175

Cross-reference
Notes on diagnostics with LEDs are found in the Chapter below.
Notes on diagnostics of I/O modules capable of diagnostics are found in the
relevant Manual.
Diagnostic buffer
If an error occurs, the CPU writes the cause of error to the diagnostic buffer. In
STEP 7 you can read the diagnostic buffer with your PG. This location holds error
information in plain text.
Other modules capable of diagnostics can be equipped with their own diagnostic
buffer. In STEP 7 (HW Config > Hardware diagnostics) you can read out his buffer
on your PG.
diagnosable modules without diagnostic buffer write their error information to the
CPU's diagnostic buffer.
When an error or an interrupt event occurs, (e.g. time-of-day interrupt), the CPU
switches to STOP mode, or you can react in the user program via error/interrupt
OBs. This would be OB82 in the above example.
Diagnostics with System Functions
If the following CPUs are used, we recommend that you use the more user-friendly
SFB 54 RALRM (called in diagnostic OB 82) to evaluate the diagnostics from
centralized or distributed modules or DP slaves:
• CPU 318-2 DP, firmware version V 3.0.0 or later
• CPU 31xC, firmware version V 2.0.0 or later
• CPU 312, firmware version V2.0.0 or later
• CPU 314, order no. 6ES7314-1AF10-0AB0, firmware version V2.0.0 or later
• CPU 315-2 DP, order no. 6ES7315-2AG10-0AB0, firmware version V 2.0.0 or
later
Further options for diagnostics with system functions are listed below:
• Using SFC 51 "RDSYSST" to read an SSL partial list or an extract thereof.
• Reading the diagnostic data (Slave diagnostics) of a DP slave, using SFC13
"DPNRM_DG"
Every DP slave provides slave diagnostic data according to EN 50 170 Volume
2, PROFIBUS. You can use SFC13 DPNRM_DG" to read these diagnostic
data. Error information is stored in hex code. Refer to the relevant module
manual for information on the meaning of the read code.
For example, the entry of the value 50H (= dual 0101 0000) in byte 7 of the
slave diagnostics for the distributed I/O module ET 200B indicates a faulty fuse
or missing load voltage in channel group 2 and 3.
• Reading a data record with SFC59 "RD_REC"
S7-300 Programmable Controller Hardware and Installation
A5E00105492-02
Testing functions, Diagnostics and Fault Elimination
11-5