Memory concept
6.4 Measured value log files
Note
The active system functions SFC 82 to 84 (current access to the MMC) have a distinct
influence on PG functions (block status, variable status, load block, upload, open, for
example).
This typically reduces performance (compared to passive system functions) by the factor
10.
in order to prevent data losses, do not exceed this maximum of delete/write operations.
Also refer to the SIMATIC Micro Memory Card (MMC) section in the "Structure and
Communication Connections of a CPU" chapter.
Caution
Data on a SIMATIC Micro Memory Card can be corrupted if you remove the card while it
is being accessed by a write operation. In this case, you may have to delete the MMC on
your PG, or format the card in the CPU.
Never remove an MMC in RUN mode. Always remove it when power is off, or when the
CPU is in STOP state, and when the PG is not a writing to the card. When the CPU is in
STOP mode and you cannot not determine whether or not a PG is writing to the card
(e.g. load/delete block), disconnect the communication lines.
6.4 6.4 Measured value log files
Introduction
Measured values are generated when the CPU executes the user program. These values
are to be logged and analyzed.
Processing sequence
Acquisition of measured values:
The CPU writes all measured values to a DB (for alternating backup mode in several DBs)
which is located in RAM.
S7-300 CPU Data: CPU 315T-2 DP
Manual, 12/2005, A5E00427933-02
6-15
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