iC-TW8 16-BIT SIN/COS INTERPOLATOR
Serial Configuration Mode
Jan 9, 2013 Page SC23/36
eration above the maximum speed shown on the AB
Configuration tab (see page 18). It is recommended
to configure fatal operational faults to latch the
FAULT output as they can result in erroneous inter-
polator output.
resolution for the adaption limits is available if the
adaption quality monitor is also used (see page 24).
If adaption faults are not used, the design tool sets
the adaption limits to their highest possible (actual)
values to avoid ever stopping auto adaption. Since
an adaption fault always latches the FAULT output
and stops auto adaption if adaption faults are used, it
is recommended not to use adaption faults without
precise knowledge of how the parameters adapt un-
der all operating conditions. Adaption faults are
cleared at restart when valid startup values for the
parameters are read from the EEPROM.
An operational warning is active if the instantaneous
sensor input velocity is greater than the maximum
speed or warning fault speed shown on the AB con-
figuration tab (see page 18). Interpolator output is
still correct while an operational warning is active.
Maximum speed is determined by the desired speed
limit (see page 18) while the warning fault speed is
always half the fatal fault speed. If operational
warnings are treated as faults, they can be config-
ured to activate or latch the FAULT output. If op-
erational warnings are not treated as faults, they are
ignored. It is recommended to configure operational
warnings to be treated as faults but not to latch the
FAULT output so that the FAULT output is de-
activated when the condition is resolved.
Finally, the design tool summarizes the conditions
that activate the FAULT output, the conditions that
latch the FAULT output, and the conditions that are
ignored. Latched faults are cleared by restarting the
iC-TW8 or by writing to the STAT_SP, STAT_EE,
or FLT_STAT registers using one of the serial ports
(see Programmer’s Reference).
An ADC fault is active if the signal input level to
the analog-to-digital converters in the AB signal
path (see page 5) is outside defined operational lim-
its. The upper signal level (called ADC overflow) is
fixed at 1.5V, which is 106% of the nominal signal
level into the ADC.
ADC Quality Monitor
If Set ADC Underflow? = No in the FAULT Pin
Configuration tab, the ADC Quality Monitor tab can
be ignored in its entirety. If Set ADC Underflow? =
Yes in the FAULT Pin Configuration tab, use the
ADC Quality Monitor tab to enable or disable the
ADC quality monitor. If the ADC quality monitor is
not used, the remainder of the ADC Quality Monitor
tab may be ignored.
The lower signal level (called ADC underflow) can
be set between 10% and 100% of nominal signal
level or left at the default (10%). Enter the desired
ADC underflow level and the design tool confirms
the closest possible (actual) level. Less resolution
for the ADC underflow level is available if the ADC
quality monitor is used (see page 23).
If the ADC quality monitor is used, enter the desired
ADC quality threshold level. This is the ADC level
in percent of nominal signal input amplitude that is
considered to be the boundary between acceptable
and marginal signal level for the application. The
design tool shows the closest possible (actual) ADC
quality threshold level and the desired and actual
ADC underflow fault levels from the FAULT Pin
Configuration tab.
ADC overflow and underflow faults are not fatal,
but interpolation accuracy is reduced when operat-
ing under these conditions. Therefore, it is recom-
mended not to latch ADC faults, but to stop auto
adaption when an ADC fault is active. This prevents
auto adaption from overcompensating for an out-of-
range input signal and de-activates the FAULT out-
put when the input signal is back in range.
In operation, the iC-TW8 continuously calculates
the variable QM_ADC as a value between 0 (ADC
level > ADC quality threshold) and 255 (ADC level
≤ ADC underflow level). Between the quality
threshold level and the underflow level, QM_ADC
is inversely proportional to the ADC level as shown
in the design tool graph. Thus, QM_ADC indicates
the relative quality (signal amplitude) of the input
signal. QM_ADC is a component of the PWM sig-
nal that drives the STATUS output (pin 19) for ex-
If adaption faults are used, enter the desired maxi-
mum adaption values for offset, gain match, and
phase. The design tool confirms the closest possible
(actual) values. When any of these levels is exceed-
ed, adaption of the corresponding parameter stops
and an adaption fault is activated (see page 21). Less
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