322
FX
3U
/FX
3UC
Series Programmable Controllers
Programming Manual - Basic & Applied Instruction Edition
13 High Speed Processing – FNC 50 to FNC 59
13.2 FNC 51 – REFF / Refresh and Filter Adjust
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
*1
in FX
3UC
PLCs. The digital filter value can be changed
within the range from 0 to 60 ms through using an instruction.
*1.
X000 to X007 in the FX
3U
-16M
1. How to change the digital filter (executing END instruction)
The input filter initial value (10 ms) of X000 to X017
*2
is set in the special data register D8020.
Accordingly, by changing this value using MOV instruction, etc., the input filter value of X000 to X017
*2
which
is used during execution of END instruction can be changed.
*2.
X000 to X007 in the FX
3U
-16M
2. Instruction in which the digital filter is automatically changed
Without regard to the change of 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
µ
s in X000 to X005 and 50
µ
s in X006 and X007).
However, if the digital filter is used for any purpose other than the following functions and instruction in a
general program, the digital filter is set to the time set in D8020. As a result, the program is not executed
correctly if the ON duration 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 high speed counter
• Input used in SPD (FNC 56) instruction
D8020
REFF
instruction
When the
command is ON
When END
instruction is
executed
X000 to X017
Input terminal
Digital filter
Initial value: 10 ms
Input image
memory
X020 and
later
Input terminal
C-R filter
Fixed to 10 ms
*2