LMC058 NV Ram

[VaughnKretzmann]

What battery is used to backup the non-volatile RAM in the LMC058 controller?

Does the RTC battery also back up the non-volatile RAM?

[SimA]

Where have you seen the mention of NVRAM for the LMC058?  I think it's only a way to say that there's some Non Volatile memory.  The LMC058 controller typically stores it's variables in RAM but the variables declared as Retain and Retain Persistent will get backed-up to flash memory when power is turned off.

The variables declared as Retain and Retain Persistent are stored in a dedicated RAM zone while the PLC is on. When it's turned off, the energy stored in a few internal capacitors is enough to transfer that data area of ​​the RAM to a non-volatile memory area (NAND Flash memory, similar to USB keys that doesn't need to be powered). That means there is no limitation on the number of write cycles of persistent variables during execution of the program.  The write cycle only happens when the controller turns off and the flash memory get written.  Like all flash memory, there's a limitation on the quantity of write cycles for the lifetime of the chip.  For the LMC058 and M258 it's rated for around 200 000 write operations and for the M241 and M251 around 2millions operations.

On power on, the Retain/Retain Persistent values ​​are copied back from flash memory to RAM before the program execution starts.

The battery is used to keep time when power is removed.  It's a non-rechargeable but replaceable battery.

Info about the RTC battery in the LMC058 Hardware Guide