PLC addressing mode

Addressing mode


Programmable controller address is encoded inside the PLC elements, so that when the program execution can uniquely identify each component. PLC in a data store for each element is assigned a storage area and letters as a regional symbol and represents the type of component. Such as: digital input and write the input image register (markers for I), digital output is written to the output mapping registers (symbol Q), writes the analog input analog input mapping registers (markers for AI), writes the analog output analog output mapping registers (markers for AQ). In addition to input/output, a PLC and other components, v represents the variable memory m that represents the internal flag bit memory; SM represents a special sign-bit memory; l for local storage; t timer c counter; HC high speed counter; s for sequential control memory AC accumulator. Master the function and use of each component is the Foundation of programming. Here‘s components addressing mode.


Storage unit can be a bit (bit), bytes (Byte), the word (Word), DWORD (Double Word), then addressing mode can also be divided into bit, byte, Word, double word address.


1. bit addressing


Address specified to: (marker) number of bytes, such as I0.0;Q0.0;I1.2.


2. Byte address


Byte address as specified: (marker) b (bytes), such as the IB0 consists of I0.0~I0.7 8-bit bytes.


3. Word address


Word address specified: (marker) w (starting byte number), and the most significant byte is the start byte. For example VW0 represents consists of VB0 VB1 and 2byte words.


4. double word address


For double word address specified: (marker) d (starting byte number), and the most significant byte is the start byte. For example VD0 VB0 to VB3 this 4byte DWORD.

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