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FX Series Programmable Controlers Applied Instructions 5
5-53
5.6.1 REF (FNC 50)
Operation:
Standard PLC operation processes output and input
status between the END instruction of one pro
g
ram
scan and step 0 of the followin
g
pro
g
ram scan. If an
immediate update of the I/O device status is required
the REF instruction is used. The REF instruction can onl
y
be used to update or refresh blocks of
8 (n) consecutive devices. The head address of the refreshed devices should alwa
y
s have its
last di
g
it as a 0 (zero), i.e. in units of 10.
5.6.2 REFF (FNC 51)
Operation:
PLC’s are provided with input filters to overcome
problems
g
enerated b
y
mechanical switch
g
ear.
However, as this involves ensurin
g
a stead
y
input
si
g
nal is received for a fixed time duration, the use of
input filters slows down the PLC response times. For hi
g
h speed applications, especiall
y
where
solid state switchin
g
provides the input si
g
nal, input filter times ma
y
be reduced. The default
settin
g
for the input filters is approximatel
y
10 msec. Usin
g
this instruction input filter times of 0
to 60 msec ma
y
be selected. The settin
g
‘0’ (zero) is actuall
y
50
µ
sec. This is the minimum
available settin
g
. It is automaticall
y
selected when direct input, interrupts or hi
g
h speed countin
g
functions are used. The REFF instruction needs to be driven for each pro
g
ram scan if it is to be
effective, otherwise, the standard 10 msec filter time is used.
Mnemonic Function
Operands
Program steps
Dn
REF
FNC 50
(
Refresh
)
å
Forces an
immediate update
of inputs or
outputs as
specified
X, Y
Note:
D should alwa
y
s be a
multiple of 10, i.e. 00,
10, 20, 30 etc.
K, H
Note:
n should alwa
y
s be a
multiple of 8, i.e. 8, 16,
24, 32 etc.
REF, REFP:
5 steps
Mnemonic Function
Operands
Program steps
n
REFF
FNC 51
(Refresh
and filter
ad
j
ust)
Inputs are
refreshed, and
their input filters
are reset to the
newl
y
desi
g
nated
value
K, H,
Note: n= 0 to 60 msec (0 = 50
µ
s)
X000 to X007 (X000 to X017 for FX
2N
) are
automaticall
y
desi
g
nated when usin
g
this
instruction
REFF,
REFFP:
3 steps
X0
X 10
[ D ]
K 8REF
[ n ]
Note:
A short dela
y
will occur before the I/O device is ph
y
sicall
y
updated, in the case of inputs
a time equivalent to the filter settin
g
, while outputs will dela
y
for their set ener
g
ized time.
X10
K 1
REFF
[ n ]