IX34208a_e.doc / Aug-09
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Bit Blanking:
If now, for example, from these 16 valid bits only the bits 3 to 12 should be used for further
evaluation, the corresponding setting would be „Hi bit“ = „17“ and „Lo bit“ = „08“.
Hi Bit
Î
Lo Bit
Î
Requested
Bits (Clocks)
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
Usable Bits
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
X
X
X
X
X
---Evaluated Bits ---
5.3. Scaling of the Display
Under consideration of the scaling parameters which have been described previously, the final
display value of the unit results from
DISPLAY
[Encoder SSI Data] [0-Position]
=
-
x
{ }
M-Factor
D-Factor
+/-
P-Factor
x
Encoder SSI data are always positive only. Where also negative values should be
indicated, this can be achieved by corresponding setting of the parameters
„0-Position“ or „P-Factor“
x
The LED display provides 6 decades. For this reason all parameter settings (including
0-Position) are also limited to a maximum range of 6 decades. SSI encoders with a
resolution of more than 19 bits will however generate SSI data with more than 6
decades. In such a case it can become difficult to set the 0-Position and the other
scaling parameters, while the mechanical encoder position is in the overflow zone
(the unit would insistently display "overflow").
To avoid this kind of problem with encoders of more than 19 bits, we recommend to
use the Bit Blanking Function and to evaluate 19 bits of all available bits only
(e.g. set Hi_Bit = 19 and Lo-Bit = 01 with a 25 bit encoder)
x
Where later you intend to use the "Round Loop" function, it is even mandatory to
blank all unusable bits.
x
Remote Reset/Set commands via keyboard or external input will overwrite the
current value of parameter „0-Position“ by the actual SSI position of the encoder.
Therefore, in the formula above, the content between the brackets { } will become
zero and the unit will display the same value as set to parameter „P-Factor“. This
scaling is also automatically stored to the Flash Prom for full data retention in power-
down state
