Saia-Burgess Controls AG
Manual Manual PCD 1 / PCD 2 Series │ Document 26 / 737 EN22 │ 2013-11-26
CPUs and expansion housings
3-45
Partitioning options for user memory
3
3.15 Partitioning options for user memory
InthePG5hardwareconguration,theusermemoryispartitionedbydefaultinto
lines of code and texts/DBs, in a way that suits most applications.
Inthecaseofalargeprogramwithfewtexts/DBsoraverysmallprogramwith
manytexts/DBs,theusercanpartitionthememorymanually.Inordertochoosean
appropriate breakdown, the following should be noted:
● thepartitioningisinto“Kbyteslinesofcode”and“Kbytestext/DBs”,wherethe
“Kbyteslinesofcode”canonlybechangedin4Kbytessteps,aseverylineof
code occupies 4 bytes
● theresultoftheformula(4דKbyteslinesofcode”)+“Kbytestext/DBs”must
equal the available user memory,
e.g. 4 × 24 Kbytes + 32 Kbytes = 128 Kbytes
● eachcharacterofatextoccupies1byte
● each32-bitelementofaDBoccupieseightbytesintheaddressrange0..3999,
and the header of the DB takes up a further three bytes
● PCD1,PCD2.M110/M120/M150:
For applications with many DBs, we recommend fitting a memory expansion unit,
so that extension memory can be configured. The DBs with addresses from 4000
that can be held there can hold more elements (16384 instead of 384), take up
less space (only 4 bytes instead of 8 bytes per element, but NB, 8 bytes instead
of 3 for the header) and the access time is substantially shorter. The extension
memory is independent of the memory partitioning and is only configurable where
an expansion unit is plugged in
● PCD2.M170/M480:
WerecommendthatDBswithaddresses≥4000shouldalwaysbeused.Thead-
dresses from 4000 that can be held there can hold more elements (16384 instead
of 384), take up less space (only 4 bytes instead of 8 bytes per element, but NB,
8 bytes instead of 3 for the header) and the access time is substantially shorter.
Example of manual partitioning of a PCD2.M150:
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