IC-TW28 Datasheet, PDF (74/80 Pages) IC-Haus GmbH – 10-BIT SIN/COS INTERPOLATOR

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POST-AB DIVIDER
Rev D2, Page 74/80
The iC-TW28 includes an optional divider after the in-
ternal ABZ output generator that can be used to reduce
(divide) the configured interpolation by a factor of 1-8.
This is useful when the desired output resolution is not
an integer multiple of the input resolution.
AB Generator
Post-AB Divider
OUTA
OUTB
For example, with an input resolution of 24 sin/cos cy-
cles per revolution, it is impossible to achieve an output
resolution of 1,024 AB cycles per revolution (CPR) with-
out the post-AB divider since (4×1024)/24 is not an
integer. The required interpolation factor in this case
is 1024/24 = 42.6. This value can be achieved, how-
ever, using an interpolation factor of 128 and a post-AB
divider value of 3 since 128/3 = 42.6. Thus, an output
resolution of 512 CPR is possible with an input reso-
lution of 24 using inter = 128 (INTER(9:0) = 512) and
div = 3 (INTER1.div = 2). See INTER1 on page 41 for
more information.
Divide by 2 shown.
Figure 44: Post-AB Divider
OUTZ
As shown in Figure 44, the Z output bypasses the
post-AB divider. Therefore, any configured synchro-
nization of the Z output to the A and B outputs may
be lost when using the post-AB divider. See Startup
Modes on page 58 for more information. Note also that
the actual width of the Z output (zwidth) in AB edges is
inversely proportional to the post-AB divider value (div).
See ZERO1 on page 42 for more information.
The post-AB divider can also be used to achieve low
value and fractional interpolation factors that are not na-
tive to the iC-TW28. The lowest interpolation factor that
can be directly programmed is inter = 2 (INTER(9:0)) =
8). Lower effective interpolation values (intereff) can be
achieved as shown below.
Value
inter
0.25
2
0.50
2
0.75
3
1.00
2
1.25
5
1.50
3
1.75
7
intereff
div
8
4
4
2
4
2
4
INTER(9:0)
8
8
12
8
20
12
28
INTER1.div
7
3
3
1
3
1
3
Table 127: Effective Interpolation
Note that the maximum AB output frequency (fab) is
inversely proportional to the post-AB divider value (div).
See INTER1 on page 41 and ABLIMIT on page 42 for
more information.