Programming Of Isochronous Mode For Motion Control Applications - Siemens SIMATIC S7-1500 Function Manual

Programming isochronous mode

6.3 Programming of isochronous mode for Motion Control applications

6.3 Programming of isochronous mode for Motion Control applications
MC-Servo, MC-PreServo and MC-PostServo OBs
The CPU-internal Motion Control functions are to control a drive. When an axis is created in
the CPU, the MC Servo OB is automatically created in the user program. This OB contains
an automatic update of the process image partitions.
If user programs are to be processed synchronized to the MC-Servo OB, integrate the user
programs in the MC PreServo or MC PostServo OBs. The SNYC_PI and SYNC_PO
instructions are not necessary.
The process image partitions are always updated as follows:
● The inputs are read prior to processing the MC-PreServo OB.
● The outputs are output after processing the MC-PostServo OB.
The runtime of the MC Servo OB must never be longer than the send clock of the
isochronous PROFINET IO system. When the runtime of the MC-Servo OB reaches the
length of the send clock, you must:
● reduce the application cycle in the properties of the MC-Servo OB
and
● extend the send clock in the properties of the PROFINET interface of the CPU
Note
The reduction ratio of the MC-Servo OB also influences the axis control of the Axis
technology object.
Interferences at the axis may not be compensated for satisfactorily by a reduction ratio that
is set too high.
Reference
You can find additional information on the above-mentioned OBs and their use in the
STEP 7 online help.
You can find examples of parameter assignment and possible settings of isochronous mode
for distributed I/O and drives in STEP 7 as FAQs on the Internet
(https://support.industry.siemens.com/cs/ww/en/view/109480489).
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Isochronous mode
Function Manual, 10/2018, A5E43884988-AA