The Way of PLC memory Access to data

1. Bit, byte, Word and double word


1-bit binary number (bit) value of 0 and 12 different, can be used to switch (or digital) of two different States, such as the contacts open and close coils powerup and powerdown. If the bit is 1, it means that the ladder diagram programming elements in coils electricity, normally open, normally closed contact closed fracture, later called the programming elements 1 status, or ON the programming elements. Reverse is also against.
8-bit binary number 1 byte (Byte), No. 0 is the lowest bit (LSB), the 7th highest bit (MSB). 1 two byte Word (Word), two words 1 double word.

2. How to access the data
(1) , access: the address of the memory cell formed by byte address and address, such as I3.2, which regional identifiers I indicates an input (Input), the byte address 3, address 2. As shown in Figure:
This access method is called byte addressing modes.


(2) byte access: IB3 input bytes (Byte) by I3.0~I3.7 the 8 bits.
(3) the word access: adjacent bytes in a Word, a two byte characters in the address must be continuous, and the low byte in a word it should be 8-bit, high byte in a word should be the lower 8 bits. IB14 and IB15 IW14 made of 1 Word, IW14 I region in identifier, w (Word), 14 as the starting byte address. IW14 IB14 should be 8-bit, IB15 should be the lower 8 bits.
(4) double word access: the next four bytes represents a double word, fourbyte addresses must be continuous. Lowest bytes in a double word it should be up to 8-bit. ID12 consists of IB12~IB15 double words, I as a regional identifier, d represents access to double word (Double Word), 12 as the starting byte address. ID12 IB12 should be up to 8-bit, IB15 should be the lowest 8 bits.


As shown in Figure:

Such as: the electric 0231, 0232, 40 students in one class, each class is divided into 5 groups, each group of 8 people.
The position: first set electric 0231 class 1th class
Bytes: electrical 0231 group
The word mode: electrical 0231
Double-word mode: electric 023



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