Device Functions; Values And Constants - Delta AS Series Programming Manual

2.2. Device Functions

The following flow chart shows the procedure for processing a program in the PLC.
Input ter minal X
Regener ating the input signal
Device memory
Proc es s in g th e prog ram
Device memory
Regener ating the output s ignal
and sending it to the output ter minal

2.2.1 Values and Constants

Name
Bit
Nibble
Byte
Word
Double word
The relation among bits, nibbles, bytes, words, and double words in the binary system is shown in the picture below.
W 1
B Y 3
N B7 N B6
b31 b30 b29 b28 b27 b26 b25 b24b23 b22 b21 b20 b19 b18 b17 b16 b15 b14 b13 b12 b11 b10

Regenerating the input signal
1. Before the program is executed, the state of the
external input signal is read into the memory location
for the input signal.
2. When program is executed, the state in the memory
location for the input signal does not change even if
the input signal changes from ON to OFF or from OFF
to ON. The input signal is not refreshed until the next
scan begins.

Processing the program
After the input signal is refreshed, the instructions in the
program are executed in order from the start address of
the program. The results are stored in the device memory.

Regenerating the state of the output
After the instruction END is executed, the state in the
device memory is sent to the specified output terminal.
A bit is the basic unit in the binary system. Its state is either 1 or 0.
A nibble is composed of four consecutive bits (for example b3–b0). Nibbles
can represent 0–9 in the decimal system, or 0–F in the hexadecimal system.
A byte is composed of two consecutive nibbles ( 8 bits, b7–b0). Bytes can
represent 00–FF in the hexadecimal system.
A word is composed of two consecutive bytes (16 bits, b15–b0). Words can
represent 0000–FFFF in the hexadecimal system.
A double word is composed of two consecutive words (i.e. 32 bits, b31–b0).
Double words represent 00000000–FFFFFFFF in the hexadecimal system.
D W
B Y 2 B Y 1
N B5 N B4 N B3
Description
W 0
B Y 0
N B2 N B1 N B0
b9 b8 b7 b6 b5 b4 b3 b2 b1 b0
Cha p ter 2 De vices
D ouble w ord
W ord
B yt e
N ib ble
B it
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