When a PLC performs input/output operations, analog control, and position control, it requires numerous data registers to store information and parameters. These data registers are 16-bit in size, with the most significant bit serving as the sign bit. For handling 32-bit data, two data registers can be combined, maintaining the same sign bit structure at the highest position.
There are several types of data registers:
1. General-purpose data registers (D0 to D199) consist of 200 points. When M8033 is turned on, these registers retain their data even after power loss. However, when M8033 is off, they lose all stored data upon power failure or when the PLC transitions from RUN to STOP mode.
2. Power-off data registers (D200 to D7999) include 7800 points. Among them, D200 to D511 (a total of 12 registers) have power-off retention capability. This feature can be adjusted via external device settings, allowing users to switch between general-purpose and power-hold registers. Additionally, D490 to D509 are reserved for communication purposes. Registers from D512 to D7999 cannot be modified by software to enable power-off hold, but their contents can be cleared manually. According to parameter settings, data registers starting from D1000 can function as file registers.
3. Special data registers (D8000 to D8255) contain 256 points. These registers are used to monitor the PLC's operational status, such as scan time and battery voltage. Some of these registers are reserved and not available for user use. It’s recommended to consult the user manual for detailed information about each special register.
4. Index registers (V and Z) are part of the Mitsubishi FX2N series PLC. They include 16 registers: V0 to V7 and Z0 to Z7, each being 16 bits. These registers serve a unique purpose, acting like index registers in microcomputers. They allow dynamic modification of component numbers. For instance, if V0 is set to 5, then D20V0 would refer to D25 (D20 + 5). Index registers can be read and written just like regular data registers. When 32-bit operations are required, V and Z can be used together, with Z representing the lower 16 bits and V the higher 16 bits.
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