Programming
Page 5-18 ABB Control - AC 31
1SBC 260400 R1001-b 06.99
4.1.13. The central unit cycle time
The central unit program executes in cycles for the duration which is defined in the "Cycle time
declaration"
system parameter. The value is expressed in milliseconds.
- For a master central unit : the cycle is between 0 and 100 ms where only multiples of
5 ms are authorized.
- For a slave or stand-alone central unit : the cycle time is between 0 and 250 ms.
When the 0 value is selected the cycle time is the minimum time which the central unit
requires for each cycle. In this case the cycle time is not constant.
Calculation of a cycle time:
The cycle time Tc can be calculated by the user by using the following equation:
Tc
≥ Tb + Tp
where Tb = the CS 31 bus transmission time
and Tp = the program execution time.
The program execution time corresponds to the addition of all the times of the functions
present in the user program (see the list of times in the annex).
In general, the program execution time for 1 000 bytes is:
0.4 ms for 100% of binary instructions
1.2 ms for 65% of binary instructions and 35% of word instructions.
The bus transmission time is calculated from the installation configuration. It requires adding
together the times of all the units on the bus. The total time for the extensible remote units is
given by adding the unit time and the times of the connected extensions.
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