iC-TW8 16-BIT SIN/COS INTERPOLATOR
Pin Configuration Mode
Jan 9, 2013 Page PC11/15
32
Setting the Maximum AB Frequency
and Lag Recovery
64
2500
finput
0.0002MHz 200Hz
Configuration input C3 sets the maximum AB out-
put frequency and determines whether lag recovery
is used or not. Choose the desired maximum AB
frequency and lag recovery setting from Table 5 and
connect the appropriate resistors to configuration
input C3 (pin 33) according to Table 1 to set the
corresponding configuration level.
If the incremental sensor input exceeds this frequen-
cy, the AB output position can no longer keep up
with the sensor position. In this case, the iC-TW8
keeps generating output pulses at the maximum AB
frequency until the AB output position either catch-
es up to the sensor position or falls behind the sen-
sor position by half a Sin/Cos input cycle, at which
point the FAULT output (pin 20) is activated
(latched low). This fault must be cleared by cycling
power to the iC-TW8.
C3
Level
11
10
9
8
7
6
5
Maximum AB
Frequency
fclock/8
fclock /16
fclock /32
fclock /64
fclock /128
fclock /256
fclock /8
Lag
Recovery
Lag recovery
enabled.
Lag recovery can be used to eliminate most of the
position lag at constant speed caused by the AB
output filter, at the expense of possible position
overshoot on stopping. With lag recovery enabled,
the AB output position “catches up” to the sensor
position during constant speed motion. However,
enabling lag recovery also causes the AB output fil-
ter response to become under-damped which can
result in position over- and undershoot with fast
sensor input position changes. This effect is worse
with more AB output filtering (configuration input
C2). At standstill, the AB output position is always
equal to the sensor position regardless of the AB
output filter and lag recovery settings.
4
3
2
1
fclock /16
fclock /32
fclock /64
fclock /128
fclock /256
Lag recovery
disabled.
0
Table 5: Configuration Input C3
In pin configuration mode, the highest maximum
output frequency of the AB outputs is fclock/8,
where fclock is the clocking frequency of the iC-
TW8 (see Providing a Clock on page 6). Lower
maximum output frequencies can be selected as
shown in Table 5 if devices connected to the iC-
TW8 (counters, PLCs, motion controllers, drives,
etc.) cannot handle its full output frequency.
Unless specifically required otherwise, it is recom-
mended to use the highest maximum AB frequency
and to disable lag recovery by setting C3 to configu-
ration level 5.
The incremental sensor input frequency (finput)
which corresponds to a given AB output frequency Serial Interfaces
can be calculated using the following formula:
The SPI and 1-wire serial interfaces of the iC-TW8
are fully active while in pin configuration mode. It
is possible to read and write to memory and observe
the current configuration. However, any changes
made to the configuration are only temporary. After
cycling power, the configuration reverts to that set
by the configuration inputs C0–C3.
AB Frequency
finput
Interpolation
Where Interpolation is the interpolation factor set
using configuration inputs C0 and C1.
For example, if fclock = 32 MHz, an interpolation
factor of 2500 is selected using C0 and C1, and C3
is at configuration level 8 (fclock/64), the maximum
AB frequency will be reached at a sensor input fre-
quency of
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