iC-TW8 16-BIT SIN/COS INTERPOLATOR
Serial Configuration Mode
Jan 9, 2013 Page SC28/36
For example, assume it is desired to have the Z out-
put pulse centered within the input cycle. In this
case, zpos should be set to a nominal value of
Analog Output Index Sensor
In applications where the incremental sensor pro-
duces multiple input cycles per revolution—such as
optical and MR magnetic sensors—an index sensor
must be connected to the ZERO inputs to qualify or
“gate” the Z output to ensure one and only one Z
output pulse per revolution. In this case, it is neces-
sary to set the switching threshold of the Z signal
path comparator, align the Z output pulse with the Z
gating signal, and program the desired length and
synchronization of the Z output pulse using the de-
sign tool (see page 21).
zwi dth[]
zpos[]180
2
and the ZERO input signal must be approximately
physically aligned (in-phase) with the COS– input.
As shown in Figure 26, the Z gating signal will meet
the index width requirement if its transitions fall
anywhere in the gray areas of the waveform.
1 Input Cycle
1 Input Cycle
SIN
COS
SIN
COS
360°
Sensor
0°
90° 180° 270° 360°
Internal
Z Pulse
Input
Angle
Z
Gating
Signal
zpos
0°
zwidth
OUTZ
Z Gating
Signal
zpos
OUTZ
OUTA
OUTB
zwidth
Figure 26: Digital Index Sensor Example
Any deviations from ideal synchronization of the
index signal to the COS– signal due to production
tolerances can then be compensated by adjusting the
nominal zpos value, if necessary.
zpos
Figure 27: Z Output With Analog Index Sensor
First, connect an analog output index sensor to the
iC-TW8 as explained on page 13. Then, in the Z
Configuration tab of the design tool, set the initial
Desired ZERO Threshold to 0, configure the re-
maining parameters as required (see page 21), and
load the complete CFG bock to the iC-TW8 using
the GUI or serial port commands.
To calibrate the ZERO threshold level, it is neces-
sary to observe the internal Z gating signal. To ob-
serve the internal gating signal, enable Index Gating
Test Mode in the Test Mode pane of the Settings tab
in the GUI or set the Enable Z Test Mode bit (ztest)
in the RB_TEST1 register in the RB Block of inter-
nal memory using serial port commands (see Pro-
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