
Starting Up the System
8-4
SIMATIC 545/555/575 System Manual
8.2 CPU Memory Configuration
The CPU user memory is user configurable. The actual ranges of memory
types depend upon how the memory has been configured. Ranges for
memory types are listed by CPU model in Table 8-1 through Table 8-7.
You can increase the memory allocated to a particular memory type, a block
at a time, up to the maximum listed. Block sizes vary with the memory type.
Refer to the table for your CPU.
For example, when you increase L-memory by one block, from 16 Kbytes to
17 Kbytes, system memory reserved for L-memory increases from 48 Kbytes
to 51 Kbytes.
The size of configurable system memory is determined by the CPU model.
You cannot configure all memory types to their maximum allocation size
simultaneously. For example, on a 545–1103, if L-memory is configured to
30 Kbytes, then S-memory cannot be configured to 32 Kbytes, because the
96 Kbytes of system memory would be exceeded.
Refer to your SIMATIC 505 TISOFT2 User Manual and SIMATIC
545/555/575 Programming Reference User Manual for additional
information on memory configuration and configuring I/O.
Table 8-1 545–1103/–1105 CPU Memory Configuration
Memory Type
Block
Allocation
Size
Memory
Required
per Block
Minimum
Size
Maximum
Size
Total Memory
Required for
Maximum Size
Default
Allocation
Total memory — — — 96 Kbytes — —
Ladder (L) 1 Kbyte 3 Kbytes 1 Kbyte 30 Kbytes 90 Kbytes 30 Kbytes
Variable (V) 1 Kbyte 1 Kbyte 1 Kbyte 32 Kbytes 32 Kbytes 1 Kbyte
Constant (K) 1 Kbyte 1 Kbyte 0 Kbytes 32 Kbytes 32 Kbytes 0 Kbytes
Special (S) 1 Kbyte 1 Kbyte 0 Kbytes 32 Kbytes 32 Kbytes 0 Kbytes
User (U) 1 Kbyte 1 Kbyte 0 Kbytes 32 Kbytes 32 Kbytes 0 Kbytes
Timer 2
*
10 bytes 10 1024 5120 bytes 10
Drum 2
*
96 bytes 2 20 960 bytes 2
Shift Register 2
*
2 bytes 10 1024 1024 bytes 10
Table Move 1
*
2 bytes 10 512 1024 bytes 10
One Shot 2
*
2 bytes 10 512 512 bytes 10
*
Number per block.
Memory
Configuration
Maximum
Configurable
Memory
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