AH500 Programming Manual *: * indicates that users can set the range of latched areas, and that the device can be set to Non-latched Area. The range of latched areas can not exceed the device range. Above all, only 32768 data registers at most can be non-latched areas. For example, users can set D50~D32817 or D32768~D65535 to Latched Areas although the default range of latched areas is D0~D32767. 2.2 Functions of Devices The procedure for processing the program in the PLC: 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: Input terminal X Regenerating the input signal Device memory Device memory Processing the program Device memory 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:
Regenerating the output signal and sending it to the output terminal After the instruction END is executed, the state in the device memory is sent to the specified output terminal. 2.2.1 Values and Constants The relation among bits, nibbles, bytes, words, and double words in the binary system is as follows. DW Double word W1 W0 Word BY3 BY2 BY1 BY0 Byte NB0 NB1 NB2 NB3 NB4 NB5 NB6 NB7 Nibble Bit 2-6 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.
b31 b30 b29 b28 b27 b26 b25 b24 b23 b22 b 21 b20 b19 b18 b17 b16 b15 b14 b13 b12 b11 b10 b9 b8 b7 b6 b5 b4 b3 b2 b1 b0