Hardware Manual PCD 1 / PCD 2 Series│Document 26 / 737│Edition EN 15│2008-07-22

Saia-Burgess Controls AG

Expansion of user memory

CPUs and expansion housings

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3.12 Expansion of user memory

3.12.1 Basics

The main reasons to expand the user memory for a PCD1/PCD2 are:

 The base memory is too small to store the user program and the texts

 The user program and the non-modifiable texts and data blocks are to be held in

Flash EPROM as a failsafe measure (the base memory is always RAM)

 The benefits of data blocks with addresses ≥ 4000 are to be used:

• up to 16,384 elements / DBs


• much lower overhead per element: 4 bytes per 32-bit value rather than 8 bytes


• much faster access

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The PCD2.M170 and PCD2.M480 are equipped with 1 Mbyte of RAM as standard;

this cannot be expanded. To minimize the risk of program loss, we recommend the

use of the optional PCD7.R400 flash card, which allows the user program to be7.R400 flash card, which allows the user program to be

backed up.

The use of EPROMs to expand the user memory is obsolete and is no longer

recommended. Working with Flash EPROMs is much more convenient (no EPROM

programming device required, behaves like RAM for the programmer) and just as

secure as EPROMs.