Program and instruction concept.

1. When designing the control panel using a programmable controller, the circuit shown in Fig. 1-2 needs to be disassembled to the circuit shown Fig. 1-3 (a) (b). Fig. 1-3 (a) shows the input / output allotment and wiring.
   The wiring needs to be done in the same manner as the conventional relay panel by the use of a screw-driver, cutting pliers, etc.
   On the other hand, Fig. 1-3 (b) shows the relative connectional of each element within the programmable controller.
   The connection of these contacts and coils can be executed by key operation of programming panel.
   The output coil (Y31) in Fig. 1-3(b), for instance, is driven through the parallel circuit composed of input relay contact (X31) and output relay contact (Y31) and series circuit composed of input relay contact (Y31).
   To perform the above connection by the key operation of the programming panel, it is necessary to use the instructions corresponding to the series connection parallel connection of contact, normally-open contact or normally-close contact, etc.
   In addition, it is necessary to provide the division of each element and number.  
   Accordingly, the instructions for the programmable controller are made up of instruction.
   Words and element No. in combination, indicating the connecting method.
   The multiple number of instructions are integrated to make up a program.
   
   (1) Program capacity and step No.
   
   A large number of instructions making up a program assigned whit sequential No, each of 
   which is called “step no”

       Step      instruction       Element

        No.                                       No.

         0            LD                    X01                    
         1            OR                    Y31                      
         2            AND                 X05                     
         3            OUT                 Y31                    

                                                                               
                                                                             

         999        END

A large number of instructions making up a program assigned whit sequential No,each of 
which is called “step no”
In the MELSEC F, series, it is possible to assign step Nos. in the range from “0” to “999”, which allows the programming a total of 1.000 instructions. It is referred to as a “Program capacity”. As explained previously, each element used in the Programmable controller is provided with a number of contacts, however, the actual number of contact
to be used will be restricted by the program capacity.

(2) Program Memory 
      A memory used to store such large number of instruction is called “program memory”
      The program memory is optionally available in the EPROM memory,
      EPROM memory, etc. in addition to the RAM memory incorporated in the programmable controller.
      - RAM memory ( built in programmable controller )
        The memory allows the instantaneous writing/reading, however, it is designed to hold the memory    content by the battery back up (built in programmable controller), as the content of memory may be lost in the event of power failure.
The memory is applicable to the test operation stage in which the program may be frequently modified.
      - EPROM memory ( type F-ROM-1 ROM cassette, option )
        The memory is used exclusively for reading, and requires the special devices (ROM writer, erase) for    writing, correction and erasing.
       Since the memory of this type is most resistible against the noise and the program once stored will not be lost, it is suitable to maintenance-free application.
-     EEPROM memory (type F-EEPROM-1 ROM cassette, option)
      The program in the memory will not be lost even in the event of power failure in the same manner as the     EPROM memory.
     The memory of this type will not require any special device for writing and erasing, which can be executed by the use of programming panel. 

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