Rockwell Automation 1761-HHP-B30 MicroLogix 1000 with Hand-Held Programmer (HHP) - Manual (Page 102)

Chapter 6
Programming Overview
6–5
The micro controller uses two devices for storing programs: RAM and
EEPROM. The RAM provides short-term storage (i.e., its data is lost on a
power down), while the EEPROM provides long-term storage (i.e., its data is
not lost on a power down). The diagram below shows how the memory is
allocated in the micro controller’s processor.
CPU
EEPROM
Backup Data
Retentive Data
Program Files
RAM
CPU Workspace
Retentive Data
Program Files
The memory device that is used depends on the operation being performed.
This section describes how memory is stored and accessed during the
following operations:
•
saving a program
•
normal operation
•
power down
•
power up
Saving a Program
A program is saved whenever you accept edits or change from RPRG mode
to RRUN, RCSN, or RSSN mode when program edits exist. When the
program is saved, it is first stored in the volatile RAM. It is then transferred
to the non-volatile EEPROM, where it is stored as both backup data and
retentive data.
Important: If no edits exist and you select the ACCEPT EDITS menu
option, no backup data is written to the controller. It remains
unchanged.
CPU
EEPROM
Backup Data
Retentive Data
Program Files
RAM
CPU Workspace
Retentive Data
Program Files
Important: If you want to ensure that the backup data is the same for every
micro controller you are using, store the program in the memory
module before saving it. Then, when making edits to the
program, load the program from the memory module.
Understanding How Programs
are Stored and Accessed