Performance
Section 3-2
27
3-2-4
I/O response time in synchronous mode
Minimum I/O response time
In synchronous data transfer mode, the fieldbus cycle is triggered immediately
following the I/O refresh of the PLC. If the fieldbus cycle has not finished
before the start of the I/O refresh, the fieldbus cycle is not triggered until after
the next I/O refresh.
The figure below shows the minimum I/O response time in synchronous
mode. The figure shows the timing at the PLC, the timing at the Master Unit,
the timing at the slave input and the timing at the slave output.
t
IN
: The Input Slave’s ON (OFF) delay
t
OUT
: The Output Slave’s ON (OFF) delay
t
BC
: The fieldbus cycle time
t
RF
: The I/O refresh time
t
PE
: Program Execution time
The minimum response time can be achieved under the following conditions:
1.
No other master is connected to the network. More masters will increase
the fieldbus cycle time due to the token rotation between masters.
2.
User defined I/O data mapping. Only map the input and output data of the
slave. This will minimise the number of words that needs to be transferred
per I/O refresh and therefore minimise the I/O refresh time.
3.
PLC cycle time is greater than the fieldbus cycle time. In this case it is
guaranteed that one fieldbus can be triggered per PLC cycle.
4.
The fieldbus baud rate is set to the highest value allowed for the attached
slaves and used cable length.
5.
The IORF instruction can be used to further decrease processing time in
the PLC program.
The minimum I/O response time that can be achieved with C200HE, -HG or -
HX and the CS1-series is approximately
8 ms + t
IN
+ t
OUT
Содержание C200HW-PRM21
Страница 1: ...C200HW PRM21 PROFIBUS DP Master Unit OPERATION MANUAL Cat No W349 E2 2...
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Страница 5: ...C200HW PRM21 PROFIBUS DP Master Unit Operation Manual Produced May 2000...
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