PLC FUNCTIONS Part-1

In This Article we are going to see PLC FUNCTIONS Part-1 (General Functions and Program Control)

plc function
RSLOGIX 5000


General Function's


No : 1

AFI : (Always False Instruction)

PLC Instruction
Always False Instruction

Description
  • Putting this instruction in a line will force the line to be false.
  • This is primarily designed for debugging programs.

Status Bits : None

Registers : None

Available on : Micrologix , PLC-5



No : 2

IIN : Immediate Input

IOT : Immediate Output

PLC instruction
Immediate Input,Output

Description

  • These functions update a few inputs and output during a program scan, instead of the beginning and end.
  • In This Example the IIN function will update the input values on 'I:001' if 'A' is ture.
  • If 'B' is true then the output values will be updated for 'O:002". 

Status Bits : None

Registers : None

Available on : Micrologix , PLC-5



No : 3

OTL : Output Latch

OUT : Output Unlatch

PLC Instruction
Output Latch,Unlatch

Description 

  • The OTL 'L' will latch on an output or memory bit, and the 'OTL' 'U' will unlatch it.
  • If a value has been changed with a latch its value will stay fixed even if the PLC has been Restarted.

Status Bits : None

Registers : None

Available on : Micrologix , PLC-5



No : 4

XIC: Examine if Closed

XIO : Examine if Open

OTE : Output Enable 

PLC instruction
Examine if closed,open

Description 

  • These are the three most basic and common instructions.
  • The input 'A' is a normally open contact (XIC), the input 'B' is a normally closed contact (XIO).
  • Both of the outputs are normally off (OTE)

Status Bits : None

Registers : None

Available on : Micrologix , PLC-5



Program Control


No : 1

JMP : (Jump)

LBL : (Lable)


Description

  • The JMP instruction will allow the PLC to bypass some ladder logic instructions.
  • When 'A' is ture in this example the JMP will go to label '2', after which the program scan will continue normally.
  • If 'A' is false the JMP will be ignored and program execution will continue normally.
  • In either case, 'X' will be equal to 'B'.

Status Bits : None

Registers : None

Available on : Micrologix , PLC-5



No : 2

MCR: (Master control Relay)

plc programming
MCR

Description

  • MCR instructions need to be used in pairs.
  • If the first MCR line is ture the instructions up to the next MCR will be examined normally.
  • If the first MCR line is not ture the outputs on the lines after will be FORCED OFF.
  • Be careful when using normal outputs is these blocks.

Status Bits : None

Registers : None

Available on : Micrologix , PLC-5



No : 3

ONS: (One Shot)

plc instruction
One Shot

Description

  • This instruction will allow a line to be true for only one scan.
  • If 'A' becomes true then output of the 'ONS' instruction will ture on for only one scan.
  • 'A' must be turned off for one scan before the 'ONS' can be triggered again.
  • The bit is used to track the previous input state, it is similar to an enabled bit.

Status Bits : None

Registers : None

Available on : Micrologix , PLC-5



No : 4

OSR: (One Shot Rising)

OSF: (One Shot Falling)

plc instruction
One Shot Rising,Falling

Description :

  • This instruction will convert a single positive edge and convert it to a bit that is on for only one scan.
  • When 'A' goes from false to ture a positive (or rising ) edge occurs, and bit 'O:001/2' will be on for one scan.
  • Bit 'B3:4/5' is used to track the state of the input to the function, and it can be considered equivalent to an enable bit.
  • The OSF function is similar to the OSR function, except it is triggered on a negative edge where the input falls from ture to false.

Status Bits : None

Registers : None

Available on : Micrologix , PLC-5



No : 5

TND: (Temporary End)

plc programming
TND

Description :

  • When 'A' is ture this statement will cause the PLC to stop examining the ladder logic program, as if it has encountered the normal end-of-program statement.

Status Bits : None

Registers : None

Available on : Micrologix , PLC-5



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