The Automation Direct Model D4-RAM-2 is a CMOS RAM cartridge. Developed for the DirectLogic 405 family, this cartridge is designed to interface directly with the central processing unit (CPU) modules of the same series. Most CPU modules for DL405 programmable logic controllers do not include integrated memory and require external cartridges like this. System memory is needed to store programming data for the CPU. Units like D4-440 include no system memory and require a cartridge, while others like D4-450 have integrated memory but not a significant amount of space. The only module that cannot accept the cartridge is the D4-430 CPU.
CMOS RAM is offered to the CPU by this cartridge. D4-RAM-2 contains 15.5K of memory for program and data storage. RAM can be written to and read from an infinite amount of times, but it does require a power source to maintain that memory. Only while the PLC is powered will the RAM maintain the saved data. If no battery backup is used, the contents of the memory will be lost once a power supply is disrupted.
Outlined storage and installation parameters should be followed to prevent any damage to the cartridge. On the back of the CPU module, a memory card slot is available. This cartridge can only be installed in that specific memory slot on the module. Be sure to install the entire PLC unit in a temperature-controlled environment to prevent any CPU or PLC damage. A detailed installation guide is available in a series manual and a device datasheet. The appropriate manual is the D4-USER-M Instruction Manual.