Retentive Ranges Tab - System Block Configuration
View the System Block to set up PLC options by using one of the following methods:
·Click the System Block button on the Navigation Bar.
·Select the View > System Block menu command.
·Click on the System Block icon in the Instruction Tree.
Click on the Retentive Ranges tab to select the areas of memory you want to retain through power cycles. Enter new values for V, M, T, or C memory and then download the modifications to the PLC.
The numerical address limits for retentive range assignments vary with the PLC model and version. Set the target PLC model for your project with the PLC > Type menu command to enable error checking and make the values loaded by the default button consistent with the actual values of the target PLC.
All V, M, T, and C memory is set as Retentive by default. You can re-define the ranges to make some memory Non-Retentive. These assignments configure the power-down power-up initialization process.
You can define up to six retentive ranges to select areas of memory that you want to retain through power cycles. You can define ranges of addresses in the following memory areas to be retentive: V, M, C, and T. For timers, only the retentive timers (TONR) can be retained, and only the current value for timers and counters can be defined as retentive. Timer and counter bits are cleared on each power-up.
The PLC has a super capacitor that maintains RAM data after PLC power is removed. Some PLC models support an optional battery cartridge that extends the time that RAM data can be retained. The battery cartridge provides power only after the super capacitor has been drained.
At power down: The first 14 bytes of M memory (MB0 to MB13), if configured to be retentive, are permanently saved to the EEPROM when the PLC module loses power.
At power-up: The PLC checks the RAM memory to verify that the super capacitor or battery has successfully maintained the data stored in RAM. If the RAM data was successfully maintained, the retentive areas of RAM memory are left unchanged. The corresponding areas of permanent V memory (in the EEPROM) are copied to the non-retentive areas of V memory in PLC RAM. The User Program and PLC Configuration are also restored from the EEPROM. All other non-retentive areas of PLC RAM are set to 0.
At power-up: If the contents of the RAM were not maintained (as after an extended power failure), the PLC clears the RAM (including both the retentive and non-retentive ranges) and sets the Retentive Data Lost memory bit (SM 0.2) for the first scan following power-up. The User Program and PLC Configuration are then copied from the EEPROM (E²) to PLC RAM. In addition, the V memory permanent area in EEPROM and the M memory permanent area (if defined as retentive) are copied from EEPROM to PLC RAM. All other areas of PLC RAM are set to 0.
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