Delta AH500 series, Hardware Operation Manual

Page: 291 / 681

A H 5 0 0 H a r d w a r e a n d O p e r a t i o n M a n u a l
5 - 6
5.2 Functions of Devices
Procedure for processing the program in the PLC:
Input ter minal X
Device memory
Processin g th e prog ram
D
ev
ice m
em
or
y
Regenerating the output signal
and sending it to the output terminal
Regenerating the input signal
Device memory

Regenerating the input signal
1. Before the program is executed, the state of the
external input signal is read into the memory of the
input signal.
2. When program is executed, the state in the memory
of the input signal does not change even if the input
signal changes from ON to OFF or from OFF to ON.
Not until the next scan begins will the input signal be
refreshed.

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, and the results are stored in the device
memories.

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.
5.2.1 Values and Constants
Name Description
Bit A bit is the basic unit in the binary system. Its state is either 1 or 0.
Nibble
A nibble is composed of four consecutive bits (e.g. b3~b0). Nibbles can be
used to represent 0~9 in the decimal system, or 0~F in the hexadecimal
system.
Byte
A byte is composed of two consecutive nibbles (i.e. 8 bits, b7~b0). Bytes can
be used to represent 00~FF in the hexadecimal system.
Word
A word is composed of two consecutive bytes (i.e. 16 bits, b15~b0). Words
can be used to represent 0000~FFFF in the hexadecimal system.
Double word
A double word is composed of two consecutive words (i.e. 32 bits, b31~b0).
Double words can be used to represent 00000000~FFFFFFFF in the
hexadecimal system.
Quadruple word
A quadruple word is composed of four consecutive words (i.e. 64 bits,
b63~b0). Quadruple words can be used to represent 0000000000000000 –
FFFFFFFFFFFFFFFF in the hexadecimal system.
The relation among bits, nibbles, bytes, words, and double words in the binary system is shown below.
b 31 b 30 b 29 b 28 b 27 b 26 b 25 b 24 b 23 b 22 b 21 b 20 b 19 b 18 b 17 b 16 b 15 b 14 b 13 b 12 b 11 b 10
b9 b8 b7 b6 b5 b4 b3 b2 b1 b0
N B0 N B1 N B2 N B3 N B4 N B5 N B6 N B7
B Y 3 B Y 2 B Y 1 B Y 0
W 1
D W
W 0
Double word
Word
Byte
Nibble
Bit