Hardware Manual for the PCD2.M5 Series│Document 26/856; Version EN 12│2014-07-24
Saia-Burgess Controls AG
Memory space on the PCD
PCD2.M5_ Classic CPUs and expansion housings
3-32
3
3.12
Memory space on the PCD
3.12.1 General
The PCD controllers are fitted with a user program memory and a matching user
backup memory as standard. On the PCD, both types are referred to as user
memory.
User Program Memory (RAM)
The user program memory consists of a RAM (Random Access Memory) and
contains the program code and a text and DB memory area. It also contains the
extension memory, which also holds DBs and texts (addresses ≥ 4000). On a PCD2.
M5_, all DBs and texts are always in RAM. The main difference between the texts
and DBs in the text/DB memory segment and those in extension memory is the
greater maximum size of DBs and texts.
To run an application on the PCD, it is sufficient to load only the user program
memory. As this is a RAM, the program and the contents of the texts and DBs (and
the other media, registers, flags etc.) may be lost if there is no power and the battery
is flat or not connected.
Backup memory (Flash)
In order to prevent the loss of the program, every PCD CPU has onboard flash
memory fitted as standard to back up the user program memory.
It is also possible to save DBs on this flash during runtime. This allows key values of
registers and flags to be saved to the flash at runtime and reloaded later.
Even with backup to the flash card, the source files for the project must be retained,
as the application is only stored in the PCD as machine code.
If it transpires when the PCD is started up that the RAM memory has been corrupted (e.g.
after a power failure with a flat or missing battery), the application is automatically reloaded
from the flash backup memory. The LIST command "Test" and operand "400" can be used to
test this.
All hardware settings are also saved to the flash backup memory (onboard or on an
equivalent flash card).
Partition of user backup memory
The user backup memory is split into two parts. The first is available for the user
program backup and is always present. In the PG5 hardware configurator, this
memory is referred to accordingly as "user program backup".