There are 3 different types of memory cards available for Q-Series PLCs and it is important to choose the correct one as they do not all support the same features. The 3 types are SRAM (RAM), Flash (ROM) and ATA (ROM).

Design Considerations

It is important to remember that adding ANY memory card to a Q-Series PLC will NOT expand the program memory. If your PLC supports 14K program steps then that is all you are going to get. Memory cards in a Q-Series PLC system can be used to gain things like more file registers or somewhere to put IEC programming symbolic information, as detailed below.


  1. Program backup means that the PLC program can be stored in ROM and loaded into RAM on the PLC startup but ultimately it still runs in the normal program RAM.
  2. File registers (R registers) are 16-bit words, thus for a 4MB memory card the maximum possible number of file registers is 2 M words (1 word = 2 bytes).

Further Information

For further information please refer to the MELSEC Q data book or contact our support desk (

You can download this Tip in PDF format here.

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