May 15, 2011

Condition Flags in Omron PLC Programming

As we discussed previously about the Internal Bits in PLC, in addition to these plc internal bits Omron PLC have some Condition flags which depicts the results of instruction execution. These special condition flag do not have a address rather they are specified with their symbols. We will see all the condition flag available for use in Omron PLC Programming.

Using Condition Flags In Omron PLC :-

The first thing we should understand is that all of the condition flags are read only and can not be also force set or force reset. Below is the list of Condition Flags in Omron PLC.

1. P_ON -->> It is always ON flag i.e it will always remain ON , this flag is used extensively as execution condition for all the Instructions which need to executed always.

2.P_Off -->> It is always OFF flag i.e it will be always off , used when we want to Stop the execution of a particular rung stopped.

3.P_ER -->> It is Error flag i.e this flag is turned ON when a error occurs i.e when the operand data in an Instruction is Incorrect. So this flag becomes high indicating that the Instruction was stopped because of incorrect operand.

4.P_AER -->> Access Error Flag . It is turned ON when an Illegal Access Error occurs. It gets High when an Instruction tries to access a particular Memory area which is Not desired.

5.P_CY -->> Carry Flag. This Flag is turned ON when there is a carry generated in Arithmetic Operation.

6.P_OF -->> Over Flow Flag. This Flag becomes high when the result of Arithmetic Operation generates a value which cant be stored by the destination Data Word.

7.P_UF -->> Under Flow Flag. Turned ON when the result of calculation underflow the capacity of the result word(s).

Apart from these above mentioned flags there are also condition flags for Equal , Greater than , less than and Not equal. These flags make it is usier to use them in PLC program for making the calculation and getting their results. As there is Compare Instruction in Omron PLC used for comparing the Value of two Data Words , so with the help of these flags we can make the further PLC Logic.

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