I/O Processing And Response Delay - Mitsubishi Electric FX3G SERIES Programming Manual

FX /FX /FX Series Programmable Controllers
3G 3U 3UC
Programming Manual - Basic & Applied Instruction Edition
6.3

I/O Processing and Response Delay

1. Operation timing of I/O relays and response delay
FX PLCs execute the I/O processing by repeating the
process (1) to process (3).
Accordingly, the control executed by PLCs contains not
only the drive time of input filters and output devices but
also the response delay caused by the operation cycle.
Acquiring the latest I/O information
For acquiring the latest input information or immediately
outputting the operation result in the middle of the
operation cycle shown above, the I/O refresh instruction
is available.
2. Short pulses cannot be received.
The ON duration and OFF duration of inputs in PLCs require longer time than "PLC cycle time + Input filter response
delay".
When the response delay of the input filter "10 ms" is considered and the cycle time is supposed as "10 ms", the ON
duration and OFF duration should be at least 20 ms respectively.
Accordingly, PLCs cannot handle input pulses at 25 Hz (1000 / (20 + 20) = 25) or more. However, the situation can be
improved by PLC special functions and applied instructions.
Convenient functions for improvement
By using the following functions, PLCs can
receive pulses shorter than the operation
cycle:
• High-speed counter function
• Input interrupt function
• Pulse catch function
• Input filter value adjustment function
6 What to Understand before Programming
(1) [Input
processing]
Input image
memory is read
(2)
Scan time
(operation
cycle)
Batch I/O method
(refresh method)
This "input ON" can be received
"Input ON" cannot
be received
OFF
ON
Program Program
processing processing
Input processing
Output processing
(
6.3 I/O Processing and Response Delay
The ON/OFF status of input
terminals is received at one time.
Input image is read,
and operation is
executed according
[Program processing]
to program.
Image memory of
each device is
updated
(3)
[Output processing]
Output
Result is
transferred to devices
output latch
are driven
memory
This "input OFF"
cannot be received
OFF
ON
Program Program
processing processing
Operation cycle
Time)
1
2
3
4
5
6
7
8
9
10
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