IC-TW28 Datasheet, PDF (69/80 Pages) IC-Haus GmbH – 10-BIT SIN/COS INTERPOLATOR

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Rev D2, Page 69/80
POSITION CAPTURE
In serial configuration mode, the full 24-bit position
value (10 bits of interpolated angle within an input cycle
plus 14 bits of multi-cycle count) of the iC-TW28 can be
captured on the rising edge of the Z output or the ZERO
input gating window and read out over the SPI port. To
use the position capture feature of the iC-TW28, the
interpolation factor must be set to 256 (INTER = 0). See
INTER1 on page 41 for more information.
ZERO0.mode = 0 (position capture on Z outputs active),
there is no uncertainly in the captured position.
After the configured capture event has occurred, the
captured position can be read via the SPI port. See
SPI Communication on page 29 for more information.
Captured position cannot be read using the Encoder
Link interface.
Select the desired position capture event using
ZERO0.mode. If ZERO0.mode = 0, the position is
captured whenever the Z outputs are activated. If
ZERO0.mode = 1, it is captured whenever the internal
Z gating window is activated. Capturing position on the
Z output is useful with distance-coded index quasi-ab-
solute systems or to ensure that the distance (angle)
between Z pulses is correct and consistent. Inconsis-
tent distance or angle between successive Z pulses
may indicate a fault in the external system. Capturing
position on the Z gating window allows the ZERO inputs
to be used for touch probe or registration applications.
The zero capture occurred (zc) bit in the SPI status byte
indicates that a capture event has occurred and that
the captured position is valid. This bit is reset after the
captured position is read.
If multiple capture events occur before the captured
position is read, the zero capture lost (zcl) bit in the
SPI status byte is set. This indicates that the captured
position from one or more previous zero capture events
has been lost. This bit is also reset after the captured
position is read.
The position value captured is the most-recently up-
dated internal position when the selected capture event
occurs. The position value is updated internally every
320 ns, synchronously with the activation of the Z out-
puts. Thus, if ZERO0.mode = 1 (position capture on Z
gating window active), the captured position may be in
error by the distance traveled during the update time. If
The host microprocessor or microcontroller can poll
the zero capture (zc) bit in the SPI status byte to de-
termine when a zero capture event has occurred. A
zero capture event can also be configured to inter-
rupt the host processor by asserting xIRQ by setting
STAT_CFG.enz = 1. See STAT_CFG on page 46 for
more information.