Hardware Manual for the PCD2.M5 Series│Document 26/856; Version EN 12│2014-07-24
Saia-Burgess Controls AG
Partitioning options for user memory
PCD2.M5_ Classic CPUs and expansion housings
3-30
3
3.10
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 appro-
priate 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 kByte steps, as every line of code
occupies 4 bytes
The result of the formula (4 x "kBytes program cells") + "kBytes texts/DBs" must
equal the effectively available user memory,
e.g. 4 x 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
We recommend always using DBs with addresses ≥ 4000. These 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:
