Rockwell Automation 1761-HHP-B30 MicroLogix 1000 with Hand-Held Programmer (HHP) - Manual (Page 103)

Chapter 6
Programming Overview
6–6
Normal Operation
During normal operation, both the micro controller and the HHP access the
program stored in the RAM. Any changes to retentive data that occur due to
program execution or programming commands affect only the retentive data
in the RAM.
The program files are never modified during normal operation. However,
both the CPU and the HHP can read the program files stored in RAM.
CPU
RAM
CPU Workspace
Retentive Data
Program Files
EEPROM
Backup Data
Retentive Data
Program Files
Power Down
When a power down occurs, only the retentive data is transferred from the
RAM to the EEPROM. (The program files do not need to be saved to the
EEPROM since they cannot be modified during normal operation.) If for
some reason power is lost before all of the retentive data is saved to the
EEPROM, the retentive data is lost. This may occur due to an unexpected
reset or a hardware problem.
CPU
EEPROM
Backup Data
Retentive Data
Program Files
RAM
CPU Workspace
Retentive Data
Program Files