Calculating The Cycle Time - Siemens CPU 31 Series Technical Data Manual

Cycle and reaction times
5.2 Cycle time
5.2.2

Calculating the cycle time

Introduction
The cycle time is derived from the sum of the following influencing factors.
Process image update
The table below shows the time a CPU requires to update the process image (process
image transfer time). The times specified might be prolonged as a result of interrupts or CPU
communication. The process image transfer time is calculated as follows:
Table 5-2
The transfer time of the process image is calculated as follows:
Base load K
Table 5-3 CPU 31xC: Data for calculating the process image (PI) transfer time
Const. Components CPU 312C
C Base load 150 μs
A Per byte in 37 μs
the rack 0
B per byte in -
module
racks 1 to 3 *
D Per word in -
(DP the DP area
only) for the
integrated
DP interface
* + 60 μs per rack
5-4
Formula for calculating the process image (PI) transfer time
+ number of bytes in PI in module rack 0 x (A)
+ number of bytes in PO in module rack 1 to 3 x (B)
+ number of words in PO via DP x (D)
+ number of words in PO via PROFINET x (P)
= Transfer time for the process image
CPU 313C CPU 313C-2 DP CPU 313C-2 PtP
100 μs 100 μs
35 μs 37 μs
43 μs 47 μs
- 1 μs
CPU 314C-2 DP
100 μs
37 μs
47 μs
- 1 μs
CPU 31xC and CPU 31x, Technical Data
Manual, 01/2006 Edition, A5E00105475-06
CPU 314C-2 PtP
-