iC-TW8 16-BIT SIN/COS INTERPOLATOR
Serial Configuration Mode
Jan 9, 2013 Page SC17/36
The iC-TW8 can be configured to use pull-up and
pull-down resistors on the sensor Sin/Cos inputs to
enhance fault detection in the event of a floating
sensor input.
AB Startup Mode determines how the AB outputs
behave when power is applied to the iC-TW8.
OUTA
Relative
AB Startup
OUTB
OUTZ
OUTA
AVDD iC-TW8
2x 2MΩ
Same Phase OUTB
AB Startup
SIN+
OUTZ
SIN–
OUTA
Burst
AB Startup
OUTB
COS+
OUTZ
COS–
Startup
2x 2MΩ
Figure 20: AB Startup Mode
AVSS
In Relative startup mode, the A and B outputs are
low on startup regardless of the sensor input posi-
tion (angle). In Same Phase startup mode, the phase
relationship of the A, B, and Z outputs is the same
after every startup as long as the post-AB divider is
not used and the actual interpolation factor, inter, is
an integer. Absolute Burst startup mode is like Same
Phase, except that the sensor position (angle) within
one input cycle is counted out on the A and B out-
puts at startup. Same Phase startup mode is the usual
selection and provides operation similar to that of a
non-interpolated encoder.
Figure 19: Input Pull-up Resistors
When input pull-ups are used and if a sensor input
becomes disconnected, that input is immediately
pulled to a level that causes an ADC fault (see page
9).
If the iC-TW8 WP (Write Protect) output (pin 29) is
connected to the EEPROM WP input (see Connect-
ing the EEPROM on page 12), then the EEPROM
can be configured to be locked (protected) or un-
locked during operation. Usually the EEPROM
should be locked during operation. To temporarily
unlock the EEPROM to store configuration and cal-
ibration data, disable EEPROM Write Protection in
the Miscellaneous pane of the Settings tab in the iC-
W8 GUI software or set the Unlock EEPROM bit in
the RB_TEST1 register in the RB Block of internal
memory using serial port commands (see Program-
mer’s Reference).
Enter the desired Counting Direction (phase rela-
tionship) for the AB outputs when sensor angle is
increasing. While it may be impossible to predict
the correct value during design, the counting direc-
tion can always be changed during testing to ensure
correct phasing.
Enter the desired amount of time for the iC-TW8 to
wait during startup for its analog circuitry to settle
(see Startup on page 14). The design tool returns the
closest possible (actual) startup delay using the cur-
rent crystal frequency.
Next, enter the desired Output Mode. AB is the usu-
al setting and configures the iC-TW8 to produce
industry-standard AB quadrature outputs. Serial and
PWM are alternate output modes that are described
on pages 30 and 31.
The CLOCK (pin 6) and FRAME (pin 8) outputs
can be activated if necessary for special applications
(see Using PWM Output Mode on page 31). In most
cases, disable the CLOCK and FRAME outputs.
Copyright © 2011–2013 iC-Haus
http://www.ichaus.com
ICHAUS [ IC-HAUS GMBH ]
