Siemens SIMATIC ET 200AL, System Manual

Page: 1967 / 2255

Functions
5.1 Isochronous mode
PROFIBUS with STEP 7 V13
70
Function Manual, 12/2014, A5E03775446-AC
Programming isochronous mode
To operate your plant in isochronous mode, the user program must be structured
accordingly. This means you have to add a synchronous cycle interrupt in the STEP 7
project tree.
You access the isochronous I/O by means of a process image partition, which means the
addresses of the isochronous modules must be located in a process image partition. You
program access to isochronous I/O with the "SYNC_PI" instructions (updating the process
image partitions of the inputs) and "SYNC_PO" (updating the process image partition of the
outputs) in the synchronous cycle interrupt OB.
You call the "SYNC_PI" instruction at the start of the synchronous cycle interrupt OB,
provided you have selected the automatic setting for the delay time. You call the
"SYNC_PO" instruction at the end of the synchronous cycle interrupt OB.
5.1.7 Diagnostics and interrupt functions
The diagnostic and interrupt functions of STEP 7 are available for isochronous mode. These
reduce downtimes and simplify localization and elimination of faults.
Events, causes of errors and remedies
Below, you will find the events for diagnostic and interrupt functions and remedies for the
problem.
Table 5- 1 Events, causes of errors and remedies
Event Cause of the error Remedy
• Synchronous cycle interrupt OB is
started with the input parameter
EventCount > 0 (number of lost OB
calls since last OB call)
If configured:
•
Call of the time error OB
• Diagnostic buffer entry "Buffer overflow
for OB6x events"
The synchronous cycle interrupt OB
takes too long.
• Shorten the synchronous cycle
interrupt OB.
•
Increase the DP cycle.
• Reduce the delay time setting
(setting with isochronous mode at
synchronous cycle interrupt OB).
Error (negative RetVals) when updating
the isochronous process image partition
with SYNC_PI / SYNC_PO:
•
Consistency warning
• Update time is after / before the
permitted access window.
SYNC_PI / SYNC_PO are not called
in the permitted access window in
the synchronous cycle interrupt OB,
which means they are called or
processed during the I/O data
transfer on PROFIBUS.
•
Increase the delay time.
•
Increase the DP cycle.
•
Adapt the program.
Error when updating the isochronous
process image partition with
SYNC_PI / SYNC_PO:
•
Access error
DP slave / module does not respond
/ is not available.