Saia-Burgess Controls AG
Manual
Manual PCD 1 / PCD 2 Series
│ Document 26
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737 E
N22 │ 2013-11-26
CPUs and expansion housings
3-45
Partitioning options for user memory
3
3.15
Partitioning options for user memory
In the PG5 hardware configuration, the user memory is partitioned by default into
lines of code and texts/DBs, in a way that suits most applications.
In the case of a large program with few texts/DBs or a very small program with
many texts/DBs, the user can partition the memory manually. In order to choose an
appropriate breakdown, the following should be noted:
● the partitioning is into “Kbytes lines of code” and “Kbytes text/DBs”, where the
“Kbytes lines of code” can only be changed in 4 Kbytes steps, as every line of
code occupies 4 bytes
● the result of the formula (4
×
“Kbytes lines of code”) + “Kbytes text/DBs” must
equal the available user memory,
e.g. 4 × 24 32 Kbytes = 128 Kbytes
● each character of a text occupies 1 byte
● each 32-bit element of a DB occupies eight bytes in the address range 0..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:
We recommend that DBs with addresses ≥ 4000 should always be used. The ad
-
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:
