iC-TW8 16-BIT SIN/COS INTERPOLATOR
Serial Configuration Mode
Jan 9, 2013 Page SC27/36
commands (see Programmer’s Reference). This
forces the internal Z gating signal onto OUTA (pin
18), as shown following, where it can be observed
using an oscilloscope.
Digital 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 align the Z output pulse with the ZERO input
signal and to program the desired length and syn-
chronization of the Z output pulse using the design
tool (see page 21).
Internal Z pulse,
once per input cycle
ZERO+
OUTZ
Delay
ZERO–
OUTA
Figure 25: Observing the Z Gating Signal
1 Input Cycle
Calibrate the Z signal path by incrementing
MAIN_ZPOS (the zpos location within an input cy-
cle) until the Z output is centered within the Z gat-
ing signal, as shown in Figure 24. MAIN_ZPOS can
be accessed using the GUI or by writing to the
MAIN_ZPOS register in the CFG block in internal
memory via the serial ports (see Programmer’s Ref-
erence). Finally, disable Index Gating Test Mode in
the Test Mode pane of the Settings tab in the GUI or
reset the Enable Z Test Mode bit (ztest) in the
RB_TEST1 register and then store the updated
MAIN_ZPOS register value to EEPROM using a
Write All command via one of the serial ports or the
Write EEPROM button in the GUI.
SIN
COS
360°
Sensor
Input
Angle
zpos
0°
Z Gating
Signal
In general, the synchronization of the index gating
signal to the Sin and Cos input signals is fixed. It is
determined by the physical alignment of the incre-
mental and Z tracks on the encoder disc or wheel
and the physical alignment of the incremental and
index sensors to each other. Since these physical
alignments cannot typically be easily adjusted, it is
important that they be carefully controlled from unit
to unit to allow interchangeability of encoder wheels
and sensors in series production.
OUTZ
OUTA
OUTB
zwidth
zpos
Figure 24: Z Output With Digital Index Sensor
First, connect a digital output index sensor to the iC-
TW8 as explained on page 13. Then, in the Z Con-
figuration tab of the design tool, set the Desired
ZERO Threshold to 0, configure the remaining pa-
rameters as required (see page 21), and load the
complete CFG bock to the iC-TW8 using the GUI
or serial port commands (see Programmer’s Refer-
ence).
To guarantee one and only one Z output pulse per
revolution, the ZERO input signal from the index
sensor must be at least as wide as the desired width
of the Z output pulse and no longer than two input
cycles minus the width of the Z output pulse under
all operating conditions. Specifically,
To calibrate zpos, it is necessary to observe both the
Z output and the internal Z gating signal simultane-
ously. To observe 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 internal memory using serial port
zwidth[] indexwidth[] 720 zwidth[]
where indexwidth[°] is the width of the index sensor
signal in input cycle degrees.
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