IC-TW8_13 Datasheet, PDF (59/63 Pages) IC-Haus GmbH – 16-BIT SIN/COS INTERPOLATOR WITH AUTO-CALIBRATION

iC-TW8 16-BIT SIN/COS INTERPOLATOR
Serial Configuration Mode
preliminary
Jan 9, 2013 Page SC32/36
Using the Post-AB Divider
The iC-TW8 includes an optional divider after the
internal AB output generation that can be used to
reduce (divide) the configured resolution by a factor
of 1–32. This post-AB divider is useful when the
desired output resolution is not an integer multiple
of the input resolution.
AB Generator
Post-AB Divider
OUTA
OUTB
The post-AB divider is also useful to allow a com-
plete range of output resolutions to be achieved us-
ing a single input resolution. For example, with an
input resolution of 128 Sin/Cos cycles per revolu-
tion, only binary output resolutions can be achieved
without using the post-AB divider. As shown in cell
B49 of the AB Configuration tab of the design tool,
resolutions between 128 and 2,097,152 CPR in in-
crements of 32 CPR can be achieved with this con-
figuration. The actual resolutions available in this
configuration (128, 160, 192, 224, 256, etc.) are
shown in the All Resolutions tab in the design tool.
Divide by 2 shown.
OUTZ
Figure 35: Post-AB Divider
When using the rotary encoder design tool to con-
figure the iC-TW8, the post-AB divider is automati-
cally enabled if necessary. The AB Configuration
tab in the design tool calculates the minimum divid-
er necessary to achieve the desired output resolution
using the configured input resolution. This mini-
mum value may be overridden if necessary by enter-
ing a divider override factor.
Entering a divider override factor of 16 in this con-
figuration provides an actual divider of 16 and re-
duces the resolution increment to 2 CPR. Now, all
even resolutions between 8 and 131,072 CPR may
be achieved. Increasing the divider override factor
to 32 allows all integer resolutions (4, 5, 6, 7, 8,
etc.) between 4 and 65,536 to be achieved using an
input resolution of 128 Sin/Cos cycles per revolu-
tion.
As shown in Figure 35, the Z output bypasses the
post-AB divider. Therefore, any configured syn-
chronization of the Z output to the A and B outputs
is lost when using the post-AB divider.
For example, with an input resolution of 24 Sin/Cos
cycles per revolution, it is impossible to achieve an
output resolution of 16,384 AB cycles per revolu-
tion (CPR) without the post-AB divider since
4 16384 24 is not an integer (see page 18). How-
ever, entering these values into the design tool gives
a minimum divider value of 3 and an effective in-
terpolation, intereff, of 682.66667. Thus, an output
resolution of 16,384 CPR is possible with an input
resolution of 24 by using the post-AB divider.
Note that the maximum speed and maximum adap-
tion speed are inversely proportional to the post-AB
divider value. Higher post-AB divider values pro-
duce lower maximum speed and maximum adaption
speed. These speed values are shown in the AB
Configuration tab of the design tool.
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