Saia-Burgess Controls AG
Manual
Manual PCD 1 / PCD 2 Series
│ Document 26
/
737 E
N22 │ 2013-11-26
CPUs and expansion housings
3-35
Expansion of user memory
3
3.14
Expansion of user memory
3.14.1 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
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 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The use of EPROMs to expand the user memory is obsolete and is no longer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.
3.14.2 Memory location of the user program, the resources, texts and DBs
Depending on whether the user memory of a PCD1/PCD2 has been expanded or
not, the memory location of various parts of the application will vary. When the user
memory is expanded by plugging in a memory chip, the user program and the text
strings/DBs with addresses < 4000 are stored in the additional plug-in chip.
The base memory provided on the CPU is then free, and can optionally be defined in
the hardware configuration as “extension memory” and used to store texts and DBs
with addresses ≥ 4000.
Memory location
Contents
No expansion of
user memory
With expansion of
user memory
Resources (registers,
flags, counters etc.)
The resources are held in a separate RAM memory on
the CPU (always in the same location, buffered by the
SuperCap or the battery)
User program
in
base memory
in additional chip in
“
USER PROG
”
socket
1)
Texts and DBs with
addresses < 4000
in
base memory
in additional chip in
“
USER PROG
” socket
1)
Texts and DBs with
addresses ≥ 4000
not available
in
extension memory
2)
1) i.e. in RAM, EPROM or Flash EPROM depending on the chip used. The use of EPROM is no longer
recommended; use Flash EPROM instead
2) Must be defined in the hardware configuration
3.14.3 Example of a memory configuration
The screenshots below show examples of the hardware configuration and associated
software settings in PG5 for a PCD2.M120 (hardware version >= J) with a 1 Mbit
Flash EPROM plug-in expansion unit (item-no. 4 502 7141 0).
