Other signal modules
7.4 Position decoder module SM 338; POS-INPUT; (6ES7338-4BC01-0AB0)
S7-300 Automation System Module data
Manual, 08/2006, A5E00105505-04
7-11
Technical data
Isochronous times for the module
In Standard Mode TWE 850 µs
TWE 620 µs
ToiMin 90 µs
TDPMin 1620 µs
In Fast Mode TWE 700 µs
TWE 0 µs
ToiMin 0 µs
TDPMin 900 µs
1
age of the encoder values determined by the transfer process and the processing
2
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):
7.4.1 Isochronous mode
Introduction
Note
The basics of isochronous operation are described in a separate manual.
Hardware requirements
To operate SM 338 in isochronous mode, you need:
● a CPU which supports isochronous mode
● a DP master which supports the constant bus cycle
● a slave interface (IM 153-x) which supports isochronous mode
Properties
SM 338 operates in non-isochronous or isochronous mode, depending on system
parameters.
In isochronous mode, data are exchanged between the DP master and SM 338 in
synchronism to the PROFIBUS DP cycle.
In isochronous mode, all 16 bytes of the feedback interface are consistent.
If synchronism is lost due to disturbance or failure/delay of Global Control (GC), the SM 338
resumes isochronous mode at the next cycle without error reaction.
If synchronism is lost, the feedback interface is not updated.
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