Special Signal modules
5-14
Programmable Logic Controllers S7-300 Module Data
A5E00105505-03
Parameters of the SM 338; POS-INPUT
You will find an overview of the parameters that you can set and their default
settings for the SM 338 in the table below.
The default settings apply if you have not performed parameter assignment in
STEP 7 (default setting bold).
Table 5-3 Parameters of the SM 338; POS-INPUT
Parameter
values Range Note
Enable
• Diagnosis interrupt Yes/no
Release parameter.
Affects all 3 channels.
Absolute value encoder
(SSI)
1)
none; 13 bits; 21 bits; 25 bits none: The encoder input is
switched off.
Code type
1)
Gray; Binary Code provided by encoder.
Baud rate
1)
,3)
125 kHz; 250 kHz; 500 kHz; 1 MHz Data transfer rate of the SSI
position decoder. Observe the
relationship between the cable
length and baud rate (see
Technical Data)
Monoflop time
1),2),3)
16 s; 32 s; 48 s; 64 ms The monoflop time is the
minimum time interval between 2
SSI message frames.
The parameterized monoflop
time must always be greater than
the monoflop time of the absolute
value encoder.
Normalization
• Places
• Units / revolution
4)
0 to 12
2 to 8192
Normalizing right justifies the
encoder values of the encoder
absolute; non-relevant places are
discarded.
Switching on freeze off; 0; 1 Designation of the digital input
whose rising edge causes a
freezing of the encoder value.
1)
See technical data of the absolute value encoder
2)
The monoflop time is the time interval between 2 SSI message frames. The parameterized monoflop
time must be greater than the monoflop time of the absolute value encoder (see technical data of the
manufacturer). The time 2 (1 / baud rate) is added to the value parameterized in HW config. At a
baud rate of 125 kHz with a parameterized monoflop time of 16 s, an effective monoflop time of 32 s
is actually achieved.
3)
The following restriction applies to the monoflop time of the absolute value encoder:
(1 / baud rate) < Monoflop time of the absolute value encoder < 64 s + 2 (1 / baud rate)
4)
to the power of two
Note
Please note that in non synchronous operation the baud rate and the monoflop
time affect the accuracy and actuality of the encoder values.
In synchronous operation the baud rate and the monoflop time affect the accuracy
of the freeze function.
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