Cycle Time Calculation - Siemens SIMATIC S7-400 Manual

9.2

Cycle Time Calculation

Increasing the Cycle Time
Basically, you should note that the cycle time of a user program is increased by the
following:
● Time-driven interrupt processing
● Hardware interrupt processing
● Diagnostics and error handling
● Communications via the MPI, PROFINET interface and CPs connected automation-
● Special functions such as control and monitoring of tags or block status
● Transfer and clearance of blocks, compression of the user program memory
● Internal memory test
Influencing factors
The following table indicates the factors that influence the cycle time.
Table 9-2
Transfer time for the process-
image output table (PIQ) and the
process-image input table (PII)
User program
execution time
Operating system scan time at
the scan cycle checkpoint
Increase in the cycle time through
communications
Impact of interrupts on the cycle
time
S7-400 Automation System, CPU Specifications
Manual, 10/2006, 6ES7498-8AA04-8BA0
system internally
(for example, Ethernet, PROFIBUS DP); included in the communication load
Factors that Influence the Cycle Time
Factors
Cycle and Response Times of the S7-400
... See table "Portions of the process image transfer time"
... is calculated from the execution times of the different
S7-400 Instruction List
instructions, see
... See table "Operating system scan time at the scan cycle
checkpoint"
You set the maximum permissible cycle load expected for
STEP 7
communication in % in
STEP 7
.
Interrupt can interrupt the user program at any time.
... See table "Increase in cycle time by nesting interrupts"
9.2 Cycle Time Calculation
Remarks
.
Programming with
, see manual
9-3