IC-TW8_13 Datasheet, PDF(54/63 Page) IC-Haus GmbH – 16-BIT SIN/COS INTERPOLATOR WITH AUTO-CALIBRATION

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IC-TW8_13 Datasheet, PDF (54/63 Pages) IC-Haus GmbH – 16-BIT SIN/COS INTERPOLATOR WITH AUTO-CALIBRATION

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iC-TW8 16-BIT SIN/COS INTERPOLATOR

Serial Configuration Mode

preliminary

Jan 9, 2013 Page SC27/36

Digital Output Index Sensor

In applications where the incremental sensor pro-

duces multiple input cycles per revolutionâsuch as

optical and MR magnetic sensorsâan index sensor

must be connected to the ZERO inputs to qualify or

âgateâ 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).

1 Input Cycle

SIN

COS

360Â°

Sensor

Input

Angle

zpos

0Â°

Z Gating

Signal

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 Programmerâs Refer-

ence).

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

commands (see Programmerâs Reference). This

forces the internal Z gating signal onto OUTA (pin

18), as shown following, where it can be observed

using an oscilloscope.

ZERO+

ZEROâ

Internal Z pulse,

once per input cycle

Delay

OUTZ

OUTA

Figure 25: Observing the Z Gating Signal

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 Programmerâs 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.

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.

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,

zwidth[ï°] ï¼ indexwidth[ï°] ï¼ 720ï° ï zwidth[ï°]

where indexwidth[Â°] is the width of the index sensor

signal in input cycle degrees.

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