What Should Be Understood Before Using Reff Instruction - Mitsubishi Electric MELSEC FX3U Programming Manual

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

13.2.1 What should be understood before using REFF instruction

Generally, a C-R filter of approximately 10 ms is provided for inputs in PLCs as countermeasures against
chattering and noise at the input contacts.
A digital filter is provided for the inputs X000 to X017
within the range from 0 to 60 ms using applied instructions.
*1. X000 to X007 in the FX
1. How to change the digital filter (executing END instruction)
The input filter initial value (10 ms) for X000 to X017
By changing this value using the MOV instruction, etc., the input filter value for X000 to X017
during execution of the END instruction can be changed.
command is ON
Input terminal
*2
X000 to X017
Input terminal
X020 and
later
*2. X000 to X007 in the FX
2. Instruction in which the digital filter is automatically changed
Regardless of the change in the filter time executed by the REFF instruction, when the following functions and
instruction are executed, the input filter value is automatically changed (to 5 µs in X000 to X005 and 50 µs in
X006 and X007).
However, if the digital filter is used in any other functions or instructions than the ones listed, the digital filter
uses the time set in D8020. As a result, the program will not run correctly if the ON or OFF duration of the
corresponding input signal is less than the input filter time.
• Input of interrupt pointer specified in the input interrupt function
• Input used in a high speed counter
• Input used in the SPD (FNC 56) instruction
360
-16M , FX
3U
REFF
D8020
instruction
When the END
When the
instruction is
executed
Digital filter
Initial value: 10 ms
C-R filter
Fixed to 10 ms
-16M , FX
3U
13 High Speed Processing – FNC 50 to FNC 59
13.2 FNC 51 – REFF / Refresh and Filter Adjust
*1
in FX PLCs. The digital filter value can be changed
3UC
-16M .
3UC
*2
is set in special data register D8020.
Input image
memory
-16M .
3UC
*2
which is used