Siemens SIMATIC S7 - Page 31

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SM 338 Equipment Manual
(4) J31069-D401-U1-A0-7618
4.3 Diagnosis Area
The errors detected by the SM 338 are stored in the 12-byte diagnosis area.
A set bit signals a n error. If the error is a sporadic one, it is stored and re-
ported to the CPU as “arriving”. After acknowledgment of the diagnosis
alarm, such an error is then immediately reported a s “departing”.
The SF LED only lights up for the actual duration of the error, but at le ast
1 second. It is switched off again t o make on-site error analysis easie r.
The P bus can only read-access the diagnosis area.
General
SF LED
(system error)
Access
D
a
t
a
Communic
a
tion with the PLC