ISO1I813T_15 Datasheet, PDF (24/57 Pages) Infineon Technologies AG – Isolated 8 Channel Digital Input with IEC61131-2 Type 1/2/3 Characteristics

ISO1I813T
Functional Description
3.6
Programmable Digital Input Filter
The sensor data and diagnosis bits of each input channel can be filtered by a configurable digital input filter. If
selected, the filter changes its output according to an averaging rule with a selectable average length. When the
sensor state changes without any spikes and noise the change is delayed by the averaging length. Sensor spikes
that are shorter than the averaging length are suppressed. Figure 16 shows the behaviour of the filter. The clock
of the Digital Filter is supplied from the internal oscillator. Therefore the filtertime depends on the oscillator
frequency setting. For the filtering times of 1.6 msec , 3.2 msec , 10 msec , 20 msec a prescaler was used.
Therefore the update interval was choosen to be 4 usec, 8 usec, 64 usec , 64 usec respectively (based on 500
kHz clock).
scan trigger
filter input
N-1
N-2
N-3
filter state
2
1
0
output is 1
output is
unchanged
output is 0
filter output
averaging time
Figure 16 Digital Filter Behavior
The averaging length is selected for each channel individually using the configuration registers COEFIL0-7. The
programmed filter time apply for both the data and the diagnostics of one channel. See Table 11 for the different
setting options including filter bypass.
Figure 17 and Table 17 describe the timing for changing filter-coefficients. Especially timing restrictions have to
be obeyed implying a minimal processing time until the new configuration and the filtered data are valid and can
e.g. be frozen with the pin SYNC. Changing the filter coefficients means resetting always the related filter.
t_filwr
t_filrd
/CS
SCLK
SDI
Wr/Adr03
Coef3
Wr/Adr04
Coef4
Rd/Adr04
XX
Rd
SDO
INPDATA
DIAG
INPDATA
DIAG
INPDATA
Coef4
t_filrdy
SYNC
SPI Mode 2
Figure 17 Filter Time Programming and Update Timing
t
Coeff _ Tim ing3. vsd
Whereas the absolute filter time depends on the internal oscillator frequency accuracy, the maximal jitter per
channel of the IC is 1.5 %. The channel jitter defined in the Figure 18 is due to the sampling error of the sensor
data with the internal clock and applies equally for all the channels.
Data Sheet
24
V 2.1, 2015-05-22