IC-TW8_16 Datasheet, PDF (61/67 Pages) IC-Haus GmbH – 16-BIT SIN/COS INTERPOLATOR

iC-TW8 16-BIT SIN/COS INTERPOLATOR
Serial Configuration Mode
Aug 16, 2016 Page SC30/36
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
zpos[°] = 180° − ^zwidth[°]
2
and the analog index sensor signal must be roughly
in-phase with the COS– input. As shown in Figure
30, 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
SIN
COS
0° 90° 180° 270° 360°
Analog
Index Sensor
Signal
zth
Z Gating
Signal
Internal
Z Pulse
OUTZ
zpos
zwidth
Figure 30: Analog Index Sensor Example
Using Serial-Only Output Mode
The iC-TW8 contains a 32-bit sensor position (an-
gle) counter that can be accessed through either of
the serial ports. Instantaneous sensor velocity can
also be accessed via the serial ports. While the serial
ports can be used to read position and velocity in all
output modes, serial-only output mode removes the
maximum AB output frequency limit, fab, allowing
higher sensor speeds. Enter Serial for the Output
Mode in the General Configuration tab of the design
tool and the A, B, and Z outputs are disabled.
Serial-only output mode is not explicitly handled in
the design tool, although the design tool may still be
used for iC-TW8 configuration. See the iC-TW8
Programmer’s Reference for information on the se-
rial ports, the 32-bit position variable POS, and the
sensor velocity variable VEL in the WM block in
internal memory.
The 32-bit position is updated at the ADC sampling
clock frequency, fadc.
fadc = ^fcore
128
To avoid jitter and aliasing when making continuous
position reads, the ADC sampling frequency and the
SPI sampling frequency must be synchronized ex-
ternally. This can be accomplished either by syn-
chronizing the iC-TW8 to the external CPU that
handles SPI communication with the TW8 or by
synchronizing the CPU to the iC-TW8.
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.
To synchronize the iC-TW8 to an external CPU, the
CPU must generate a signal derived from its own
clock to drive the iC-TW8’s clock input (pin
XOUT). The CPU must then read the 32-bit position
from the iC-TW8 at an integer divisor of fadc.
To synchronize an external CPU to the iC-TW8, set
MAIN_CFG.clockout = 1 to output the ADC sam-
pling clock on the FRAME pin. This signal can then
be used as an interrupt to the CPU to trigger an SPI
position read. Alternatively, the iC-TW8’s DSM
clock on the CLOCK output pin can be used to di-
rectly clock the external CPU. In this case, the CPU
must then read the 32-bit position from the iC-TW8
at an integer divisor of fadc.
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