Technical data

SFCs and SFBs for Updating the Process Image and Processing Bit Fields
System Software for S7-300/400 System and Standard Functions - Volume 1/2
14-6 A5E00709327-01
14.4 Updating the Process Image Partition in a
Synchronous Cycle with SFC 127 "SYNC_PO"
Description
With SFC 127 "SYNC_PO” you can update a process image partition output table
in a synchronous cycle. A user program linked to a DP cycle can use this SFC to
synchronously update output data located in a process image partition and
consistently transmit them to I/O devices.
SFC 127 can be interrupted and can only be called in OBs 61, 62, 63 and 64.
In order to ensure reliable execution of SFC 127, the following conditions should be
met (only for S7-400):
• DP clock cycle > approx. 5.0 ms
• Slave update time < DP clock cycle - 4.0 ms
Note
A call of SFC 127 "SYNC_PO" in OBs 61 to 64 is only permitted if you have
assigned the affected process image partition to the associated OB in HW Config.
A process image partition you update with SFC 127, When you update an output
process image partition with SFC 27, you may not update it with SFC 27
"UPDAT_PO" as well.
!
Caution (only for S7-400)
Avoid direct access (e.g. L PEB commands) to areas of process image partitions
you are processing with SFC 127.
If you ignore this rule, your write attempt may fail
Parameters
Parameter Declaration Data
type
Value range Default Meaning
PART INPUT BYTE 1 to 30 Number of the process
image partition output
table to be updated in a
synchronous cycle.
RET_VAL OUTPUT INT If an error occurs while
processing this function,
the return value contains
an error code.
FLADDR OUTPUT WORD Address of the first byte
to cause an error.