Instruction Set 1 Of PLC

Instruction

In this chapter we will discuss the basic instruction set. It can divided into three categories which are as follow.

Bit instruction

beat instructions operate on a single bit of data the processor means it or reset the beat the best on the logical continuity of ladder  during an operation a bit can be address as many time as the program required instruction are commonly used with output input file status filebeat file timer file counter find sequence file.

Examine if closed (XIC )

This instruction is equivalent to the normal open instruction. It is used in the ladder program to determine if a bit is ON.during the execution is the excise instruction is on or logical even when the instruction is evaluated as true. during the execution if the excise instruction is off or logical is zero then the instruction is equivalent as false.

Examine if open (XIO)

this instruction is evaluate to normally closed instruction it is used in logical program to determine if a bit is off during the execution if the excise instruction is off or logical is zero then the instruction is evaluated Astro during the execution in the access instructions on on the logical even then the instruction is evaluated as false.

Output Energized (OTE) Instruction

Anu Te structure is used in the ladder program to turn update on winter and condition are evaluated as to a bit of winter and condition are evaluated as false.

Output latch ( OTL )

this is not a type of output instruction and OTL can only turn on a bit while OTL can only turn off a bit. This instruction is along with unlatch instruction with both instruction address in the same bit.when an address is assigned to the instruction that corresponds to the address of physical output output device via to this terminal is energize when the bit is set.

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File Structure and Addressing Format of PLC

Introduction

The SLC 500 based system can be configured with or without rack system. The SLC500/PLC-5 can be configure on various sizes of rack system with different number slots. 

The micrologix 1000 and micrologix 1200 based PLC system are shown in figure. In these PLC's there is no need of rack system where Input and output are present at slot 0 for configuration.

      The SLC 500 based system user memory is comprised of data files an program files. The data file 3 through 8 are the default values. Files 9 to 255 can be configure to be bit timer, counter , control, integer , floating point, ASCII , or string files.

Output and Input data files 

The data files 0 or 1 represent external Output and Input , respectively. Table Explain the Addressing Format for Output and input.  The format specifies  e as the slot number and s as word number.

Example:- SLC 5/03 I/O addressing

1. O:2/5 means digital Output of 5 slot 2.
2. O:2 means digital output word 0 of slot 2.
3. I:1/6 means digital input 6 of slot 1.

Status File 

The addresing format of individual bit and complete word in status file. User cannot alter the Status file. To be more precised no addition or deletion is possible in content of status file.

Example:-

S:1/15 means element 1 bit 15. This is the first pass bit which can be used to initiate instruction in program.

Bit Data File 

The default representation of bit file is B3: where any file between the 9 to 255 can be made as bit file if required. The addressing format of individual bit and complete word shown. These file is used the bit instructions, shifht registers and sequencers. The maximum the size of the file is 256 one-word element with a total of 4046 bits. These bit can be used by specifying the element number i.e., 0 to 255 and the bit number i.e. , 0 to 15 within the elements. These bits can also be specifies by numbering them in sequence from 0 to 4095.

Example :-

1. B3:6/15 means bit 12 of element 6.

2. B3:254/6 means bit 6 of element 254.

Timer Data File 

The default representation of timer file is T4: where's  any file between 9 to 255 can be made as timer file if required. The addresing format of individual bit and complete word in timer file is already explained.

        Timer instruction used three control bits. Each data file is made of 3 words data file element. Word 0 is the status word , Word 1 indicate the present Value, and Word 2 indicate the accumulator Value.

Example:-

1. T4:0/15 or T4:0/EN means Enable bit.

2. T4:0/14 or T4:0/TT means timer timing bit.

3. T4:0/13 or T4:0/DN means done bit.

4. T4:0.1 or T4:0.PRE means present Word.

Counter Data File Element

The default representation of counter file is C5 : whereas any file between 9 to 255 can be made as counter file of required. The addresing format of individual bit and complete word in counter file . Each counter address is made of a 3 - word data element. Word 0 is the status word, Word 1 indicate the present value and Word 2 indicate accumulator Value.

Example:-

1. C4:0/15  means counter up bit.

2. C4:0/14 means counter down bit.

3. C4:0/13 means done bit.

4. C4:0/12 means overflow bit.

5. C4:0/11 means underflow  bit.

Control Data File 

The The default representation of counter file is C5 : whereas any file between 9 to 255 can be made as counter file of required. The addresing format of individual bit and complete word in counter file . Each counter address is made of a 3 - word data element. Word 0 is the status word, Word 1 indicate the present value and Word 2 indicate accumulator Value.

Example:-

1. R6:3/15  means enable bit.

2. R6:3/14 means unload Enable bit.

3. R6:3/13 means done bit.

4.R6:3/12 means stack empty bit.

5. R6:3/11 means error  bit.

Integer Data File

The The default representation of integer file is N5 : whereas any file between 9 to 255 can be made as integer file of required. The addresing format of individual bit and complete word in counter file . 

Example:-

1. N7:3/15  means bit 15 of element 3.

2. N7:3 means element 3 of integer 7.

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PLC Inputs and Output

PLC Input

The input interface is the circuitry , which connect the PlC input terminal to the Processor .

Typically input signal to the PLC are provided from:

1.Sensor

2. Push Button

3.Toggle Switch

Sensors:-

These are used to detect the presence of a component.

Push Button

These are used to start or stop a process.

Toggle Switches

These are used to give a constant high or low output. These Switches may also provide inputs to PLC . All of these inputs however are either present or not present. The PLC only connected with ON or OFF signal at its input. 

The interface is used to convert input signal AC to DC from these input device to low level DC voltage signal that is used in the Processor.The interface may also have to provide electrical isolation to prevent noise and the voltage spikes on the input lines from distorting the input signal .

PLC Output

The output Interface is an electronic circuitry , which connect the processor to the PLC output terminal. These output terminal are connected to the plant to control the different output like Indicator, Motor Starter, Valves and Hooters.

Learn more about plc click on link https://plcexplanation.blogspot.com/2019/12/plc-architecture-component-plc-like_22.html

Indicator:-

These are used to indicate the start or stop of a process .

Motor Starter:-

It is used to change the state of a motor from ON or OFF .

Valves:-

These used to change the state of valve from ON or OFF .

Hooters :- 

These are used to indicate the alarm occurred during the process.

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PLC Architecture & Component

Plc Architecture & Component

The PLC like a computer ,employs a microprocessors chip to the processing and memory chips to store the program. The PLC consist of :

1. A Processor                       2. Memory

3. Inputs                                 4. Output's

5. Programming Devices    6. Power Supply

The input and the Output are connected via proper interfaces. Each input and output has its own address. an interface a medium where two system come together and interface or communicate, i.e., communication between the plant being controlled and the PLC. Figure 1 shows the basic Architecture of a PLC. it contains a Processor e.g. a microprocessor chip and memory chips. It also contains all the input and output interfacing. The programming devices can be either handheld or desktop which are remote from the PLC .

1.Processor :-

Very small microprocessors - integrated circuits with the tremendous computing capacity and also controlling capacity-provide the intelligence of today's programmable controllers. The processor unit contain a microprocessors chip e.g , ZigLog Z80,8085,8086 or any 16 or 32 bit microcontroller and necessary circuit to communicate with the device inside the PLC as well as outside the PLC. This word length effect the speed at which the Processor perform most operation. 

For example :- a 32-bit microprocessor can manipulate data faster than a 16 -bit Microprocessors.

Learn More about PlC click on below link PLC Input and Output

2. Memory

The memory system is area in PLC's CPU ,where all the sequence of instruction , or programs , are stored and executed by the Processor to Provide the desired control of Feild devices. PlC memory contain RAM, and EEPROM in varying amount depending upon the design and the use of PLC.  PlC memory, generally, is divided into five major application. Specifying the right amount of memory can save costs of hardware and time associated with adding additional Memory capacity later. 

These five type of memories are:

1. Executive Memory.   2 .System Memory

3. I/O Status Memory.   4.Data Memory

5. User Memory

Memory :-

The executive memory is a collection of permentally stored program that are consider part of the PlC itself. These  supervisory program direct all system activities, such as executive of the control program and communication with the peripheral devices. Executive program are nothing but the operating system which are placed in EPROM and these rarely need any change later on. The function of executive program are :-

(a) It instruct microprocessor to examine each user instruction.

(b)It convert high -level instruction into machine level instructions.

(c) If the user program required data from other area of memory, the executive instructs the microprocessor to collect those requested data.

(d)It provide all the system status and operating condition to the microprocessor.

(e) It solve the user logic program.

(f) It update all Output device accordingly.

In short, the executive program is a special machine level program that literally runs the PlC.

2. Status Memory

While performing various functions, the executive requires a place to store intermediate result and information. The system memory is allotted for the user of the executive only and not available to user.

3. I/O Status Memory 

During each scan, the executive instructs microprocessor to read the correct statuses of the input and then information is stored in "input image area". After solving user logic program, various Output device status are generated and are stored in" Output image area ". This area of memory always available for the user for monitoring and use. User van modify those statuses only through programming.

4. Data Memory

Random access memory does not retain it's contents of power is losed; therefore ,it is a volatile type of memory. Random access memory normally uses a battery backup to sustain it's contents in the event of power outage .

RAM is allocated for the timer, counter ,math and data function to store.

 5.User Memory

This is allocated for storage of user program. The executive has to scan this area to find the user instruction. If ASCII messages or some special subroutines are there , then Processor can allocate portion of this area for storage of those special programs.

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