Other signal modules
7.4 Position decoder module SM 338; POS-INPUT; (6ES7338-4BC01-0AB0)
S7-300 Automation System Module data
7-16 Manual, 08/2006, A5E00105505-04
Parameters Range of values Note
Monoflop time
1),2),3)
16 µs; 32 µs; 48 µs; 64 µs The monoflop time represents the
minimum interval between two SSI
frames.
The configured monoflop time must be
greater than the monoflop time of the
absolute value encoder.
Scaling
• Places
• Steps per revolution 4
0 to 12
2 to 8192
Scaling right-aligns the encoder value
in the address space; irrelevant places
are discarded.
Enabling the Freeze function off; 0; 1 Definition of the digital input that
initiates freezing of the encoder value
at the positive edge.
1
See the technical data of the absolute value encoder
2
The monoflop time is equivalent to the interval between two SSI frames. The configured monoflop time must be greater
than the monoflop time of the absolute value encoder (see the technical data of the manufacturer). The time 2 (1 /
transmission rate) is added to the value set in HW Config. A transmission rate of 125 kHz and configured monoflop time of
16 ms sets an effective monoflop time of 32 ms.
3
Restriction of the monoflop time of the absolute value encoder:
(1 / transmission rate) < monoflop of the absolute value encoder < 64 µs + 2 x (1 / transmission rate)
4
to powers of two
Note
Please note that in asynchronous mode, the transmission rate and monoflop time affect the
accuracy and update quality of the encoder values. In isochronous mode, the transmission
rate and monoflop time have an influence on the accuracy of the freeze function.
7.4.4 SM 338; POS-INPUT addressing
Data areas for encoder values
The SM 338 inputs and outputs are addressed beginning at the module start address. The
input and output address is determined in your configuration of SM 338 in
STEP 7
.
Input addresses
Table 7-4 Table 5-4 SM 338; POS-INPUT: Input addresses
Encoder input Input address (derived from configuration) + address offset
0 "Module start address"
1 "Module start address" + 4 byte address offset
2 "Module start address" +8 byte address offset
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