Extended instructions
9.9 Recipes and Data logs
S7-1200 Programmable controller
System Manual, V4.2, 09/2016, A5E02486680-AK
527
Determining load memory free space
The amount of load memory free space varies during normal operations as the operating
system uses and releases memory. Use the following steps to view the load memory
memory size.
1. Establish an online connection between STEP 7 and the target S7-1200 PLC.
2. Download the program that controls your data log operations.
3. Create any optional user-defined Web pages that you need. The standard Web pages
that access data logs are stored in PLC firmware and do not use load memory.
4. Use the Online and diagnostic tools (Page 1309) or the Web server Diagnostics page
(Page 1019)to view total load memory size and free space.
Calculating the size of a data log file (all data records)
When the data log file is created the CPU allocates the maximum memory size. In addition to
the size required for all the data records, you must include storage space for a data log
header (if used), time stamp header (if used), record index header, and the minimum block
size for memory allocation.
Use the following formula to determine the size of your data log files and ensure you do not
violate the maximum size rule.
Data log data bytes = ((data bytes in one record + time stamp bytes + 12 bytes) * number of
records)
Data log header bytes = header character bytes + 2 bytes
● No data header and no timestamps = 7 bytes
● No data header and timestamps (has a timestamp header) = 21 bytes
● Data headers and no timestamps = number of character bytes in all column head text
including separator commas
● Data headers and timestamps (has a timestamp header) = number of character bytes in
all column head text including separator commas +21 bytes
Data log data bytes = ((data bytes in one record + time stamp bytes + 12 bytes) * number of
records)
Data bytes in one data record
The DataLogCreate DATA parameter points to a structure that assigns the number of data
fields and the data type of each data field for one data log record.
Multiply the number of occurrences for a given data type by the number of bytes required.
Repeat the process for each data type in a record and sum all the data bytes to get the total
of all data elements in one record.
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