Performance
Section 3-2
24
3-2-2
PLC cycle time
The PLC cycle time mainly depends on the size of the PLC program and the
I/O refresh time of the units.
The size of the PLC program is application specific. Besides optimising the
PLC program, the program execution time can only be decreased by using a
faster CPU.
The total I/O refresh time depends on the types of units that are mounted on
the Backplane(s). Not all units refresh the same amount of data.
The I/O refresh time of the C200HW-PRM21 depends on the number of data
areas and the number of I/O data words that have been mapped.
The I/O refresh time of the C200HW-PRM21 Unit can be calculated with the
following formulas.
C200HS:
t
IORF
= 1.6 + 0.4 x na + 0.067 x nw [ms]
C200HE, C200HG, C200HX, CS1:
t
IORF
= 1.0 + 0.4 x na + 0.018 x nw [ms]
where: na
= number of mapped data areas
nw
= number of mapped I/O words (na
≥
1)
Using the default mapping mode, the I/O refresh time is:
C200HS
: 6.7 ms (2 areas: 32 words out, 32 words in)
C200HE,
C200HG,
C200HX,
CS1-series
: 3.6 ms (2 areas: 50 words out, 50 words in)
Refer to the Operation Manual of the CPU for more detailed calculations of
the PLC cycle time.
Note
The I/O refresh time is not constant over all PLC cycles. During an I/O
refresh, the unit can transfer I/O data, slave status information, and IR words
(control & status). IR data is always transferred. I/O data and slave status
data are only transferred under certain conditions:
Input data:
Only when there is new input data available. The
situation that there is no new input data occurs when the
fieldbus cycle time is greater than the PLC cycle time or
when the communication is inhibited.
Output data:
Always transferred after the Unit is initialised, except
during a download and in the synchronous mode when
the fieldbus cycle time is greater than the PLC cycle time.
Slave Status:
Always transferred after the Unit is initialised.
Summary of Contents for C200HW-PRM21
Page 1: ...C200HW PRM21 PROFIBUS DP Master Unit OPERATION MANUAL Cat No W349 E2 2...
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Page 5: ...C200HW PRM21 PROFIBUS DP Master Unit Operation Manual Produced May 2000...
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Page 66: ...Debug mode Section 4 4 50...
Page 98: ...Messages Section 6 4 82...
Page 108: ...Maintenance Section 7 3 92...
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