IC-TW28 Datasheet, PDF (58/80 Pages) IC-Haus GmbH – 10-BIT SIN/COS INTERPOLATOR

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Rev D2, Page 58/80
STARTUP MODES
In serial configuration mode, the START.mode regis-
ter value determines how the AB outputs behave at
startup. START.mode is only effective if the incremental
ABZ outputs are enabled (OUTPUT.abzen = 1). If OUT-
PUT.abzen = 0, the START.mode value has no effect.
Prior to startup, the AB outputs are in a high-impedance
state regardless of the startup mode.
In relative startup mode, the A+ and B+ outputs are
both 0 after startup because OUTPUT.apol = 0 and
OUTPUT.bpol = 0.
Value
0
1
2
3
START.mode (0x4001 Bits 4:3)
Description
Relative startup mode
Same phase startup mode
Absolute burst startup mode
Reserved (do not use)
Table 121: Startup Mode
In relative startup mode, the state of the A+ and B+ out-
puts is always the same after startup, regardless of the
sin/cos inputs (sensor angle). In same phase startup
mode, the state of the A+ and B+ outputs at a given
sensor angle is always the same after every startup.
This is similar to the operation of a non-interpolated en-
coder. Absolute burst startup mode is like same phase,
except that the sensor angle within an input cycle is
counted out on the A and B outputs at startup.
For example, Figure 32 shows the AB output behavior
in the three different startup modes with inter = 9, OUT-
PUT.apol = 0, OUTPUT.bpol = 0, and a sensor angle of
70^◦ with no motion at startup.
Relative
A+
Startup Mode _B+
Same Phase ^A+
Startup Mode _B+
In same phase startup mode, the A+ output is low and
the B+ output is high after startup since these are the
states that correspond to an input sensor angle of 70^◦
with inter = 9.
In absolute burst startup mode, the A+ and B+ out-
puts are both 0 at the beginning of startup (because
OUTPUT.apol = 0 and OUTPUT.bpol = 0) and then 7
AB edges are generated, leaving the A+ output low
and the B+ output high (the same as in same phase
startup mode). With inter = 9, each AB edge repre-
sents 360^◦/(9×4) = 10^◦ of the input sin/cos cycle. Thus
70^◦/10^◦ = 7 AB edges are required to represent the
sin/cos sensor startup angle of 70^◦.
In all startup modes, the actual state of the outputs after
startup can be changed using OUTPUT.apol and OUT-
PUT.bpol. See Output Modes, Directions, and Polarities
on page 56 for more information.
Same phase startup mode should only be used if IN-
TER1.div = 0, 1, 3, or 7 (post-AB divider disabled or
power of 2), and inter is an integer. If INTER1.div = 2,
4, 5, or 6, or inter is not an integer, then the state of
the A+ and B+ outputs at a given sensor angle are not
always be the same during operation.
In absolute burst startup mode, a maximum of 2×inter
AB edges (±180^◦) may be generated during startup.
These edges are output at a rate determined by the
value of the ABLIMIT register.
Absolute Burst ^A+
Startup Mode _B+
In pin configuration mode, same phase startup mode
with OUTPUT.apol = 0 and OUTPUT.bpol = 0 is used,
as shown in Figure 32.
Startup
Begins
Startup
Ends
Figure 32: iC-TW28 Startup Modes
Z+