Special Signal modules
5-12
Programmable Logic Controllers S7-300 Module Data
A5E00105505-03
Example of normalization of an encoder value
You are using a single-turn encoder with 2
9
units= 512 units/ revolution
(resolution/360°).
In STEP 7 you have set the following parameters:
• Absolute encoder: 13 bits
• Normalization: 4 places
• Units / revolution: 512
Before the normalization: cyclically acquired encoder values 100
0
31
0000 00000000 0000000000000
XXXX
00100
11
0000
Transferred bits
Relevant bits
After the normalization: encoder values 100
0
31
0000 00000000 0000000000000 001001100000000
Relevant bits
Double data word
Double data word
Result: Bits 0 to 3 (4 places, marked with “x”) are omitted.
5.4.7 Freeze Function
The freeze function “freezes” the current encoder values of the SM 338. The
freeze function is coupled to the digital inputs DI 0 and DI 1 of the SM 338.
The freeze is triggered by an edge change (rising edge) on DI 0 or DI 1. A frozen
encoder value is identified by the bit 31 (output address) being set. With a digital
input you can freeze one, two or three encoder values.
You must switch on the freeze function, i.e. set the corresponding parameters in
STEP 7 .
The encoder values are retained until the freeze function is ended and can thus be
evaluated dependent on the event.
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