iC-TW8 16-BIT SIN/COS INTERPOLATOR
Pin Configuration Mode
Jan 9, 2013 Page PC14/15
undetectable during encoder operation, even with
heavy filtering.
Finally, the design tool shows the conditions which
activate or latch the FAULT output (pin 20).
Latched faults are cleared by cycling power to the
iC-TW8.
Speed overshoot is calculated as a percent of speed.
Speed overshoot is typically noticed at the end of
the acceleration ramp (the beginning of the constant
velocity portion of the motion profile). Speed over-
shoot as a percent of speed is affected only by the
selected AB filter level and whether or not lag re-
covery is used. The actual amount of speed over-
shoot in RPM is proportional to encoder speed.
Pin Configuration Reference
At power-on, the four configuration input levels
(C0–C3) are read and used to set internal variables
of the iC-TW8 to the proper values. Other internal
variables are also set to specific values and cannot
be changed using the configuration inputs. Table 6
provides a list of the internal variable values used in
pin configuration mode as a reference for trouble-
shooting or new applications. Variables not listed in
the table are set to 0. Detailed information on all iC-
TW8 internal variables is available in the Serial
Configuration manual.
Next, enter the desired AB output hysteresis in AB
edges. The design tool calculates the equivalent hys-
teresis in degrees of a Sin/Cos input cycle. Hystere-
sis is used to prevent instability (dithering) of the
AB outputs at standstill due to noise. In general, use
the lowest hysteresis that produces stable AB out-
puts with no sensor motion.
Value
iC-TW8 Variable
(pin configuration mode)
Next enter Yes or No as to whether an index sensor
is used. If an index sensor is not used, the ZERO
inputs of the iC-TW8 should be connected to
AVDD and AVSS as explained on page 5. If an in-
dex sensor is used the width of the Z output pulse is
shown. The Z output pulse is always one AB edge
(one quadrature state) wide in pin configuration
mode. The Z output is synchronous with A and B
low when an integer interpolation factor is used. Not
using an index sensor allows higher speeds with
high interpolation factors.
MAIN_CFG
MAIN_INTER
MAIN_HYST
MAIN_FLTR
MAIN_OUT
wp = 1
Determined by C0 and C1.
Determined by C2.
Determined by C2 and C3.
start = 10 (0x0A)
xtal = 1
MAIN_CLOCK
div = 3
AB_CFG0
AB_VTOP
ADPT_CFG
startmode = 1
Determined by C3.
Determined by C1.
flimit = 6
ADPT_DETAIL
tbase = 4
prop = 2
offtol = 2
gaintol = 2
limit = 10
limit = 10
limit = 10
vwarn = 1
long = 1
Enter the desired auto-adaption mode for the iC-
TW8. Auto-adaption refers to the iC-TW8’s ability
to track and change (adapt) sensor gain, offset, and
phase during encoder operation to maintain low AB
output error and jitter under all operating conditions.
One of four auto-adaption modes can be selected
and the design tool confirms which iC-TW8 param-
eters are adapted during operation. Regardless of the
selected mode, auto-adaption is disabled above the
displayed speed. In pin configuration mode, the
maximum auto-adaption speed is fixed and depends
on the selected maximum speed, crystal frequency,
and interpolation factor.
ADPT_CORR
MON_OFF
MON_GAIN
MON_PHASE
FLT_CFG
FLT_EN
ee = 1
vfatal = 1
Table 6: Pin Configuration Reference
At this point, the iC-TW8 configuration is complete-
ly specified and the configuration resistor values
necessary to achieve this configuration are shown.
See Figure 11 on page 2 for a schematic of the elec-
trical connection of the resistors to the iC-TW8. Al-
so shown is a jumper map for setting the TW8_1D
demo board to the selected configuration.
Copyright © 2011–2013 iC Haus
www.ichaus.com
ICHAUS [ IC-HAUS GMBH ]
