Ip251_02b_oi_e.doc / Apr-16
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Parameter
Description
SSI Low Bit:
SSI High Bit:
Defines the lowest bit (LSB) for evaluation when the bit blanking function
is used. Must be set to “01” for full evaluation of the encoder range.
Defines the highest bit (MSB) for evaluation when the bit blanking function
is used. Must be set to the total number of encoder bits for full evaluation
of the encoder range.
The following example uses a 13 bit encoder where High Bit is set to 12 and
Low Bit is set to 03, resulting in evaluation of bits 03 to 12 and blanking of positions
01, 02 and 13
13 12 11 10 09 08 07 06 05 04 03 02 01
(Hi_bit = 12, Lo_bit = 03)
evaluated bits
(LSB)
(MSB)
Most significant bit
Least significant bit
Bit blanking results in a different evaluation of the encoder information,
and you should be fully aware of what happens with the resolution and
the number of registered turns when you use this function. The
subsequent example uses a 13 bit single-turn encoder to explain
different result with blanking on one bit:
Without blanking, a 13 bit encoder would provide a 0
...
8191
information with a 0
...
360º turn of the encoder shaft.
This assumes setting of “High Bit = 13” and “Low Bit = 01”.
It is easy to understand that there are two different ways how to use
only 12 of the 13 bits available:
When we set High Bit to 12 while Low Bit remains 01, we have
blanked the high order bit. The result corresponds to an encoder
providing information 0
...
4095 while we turn from 0
...
180º, and
again the same 0
...
4095 information while we turn from 180º to 360º.
The resolution remains unchanged with respect to the number of steps
per revolution.
We can also leave High Bit to 13 and set Low Bit to 02 instead.
This means blanking the low order bit. As a result, within one turn
of 0 ... 360º, we receive the encoder information 0 ... 4095 one time
only, but the total number of steps per revolution has been halved.
