Chapter 17

Comparison and Data-handling Instructions

Objectives

• Describe the function of the common comparison instructions.

• Explain the difference between a move instruction and a copy instruction.

• Determine the data resulting after execution of a masked move instruction.

• Explain how a copy instruction can be used to copy recipe data from one source to another.

• Explain which instruction to use to have the PLC convert from an integer to a BCD value or from a BCD value to an integer.

Comparison Instructions

• Input instructions that test the relationship between two values, source A and source B– Source A is an address.– Source B can be an address or a constant

value.

Equal Instruction (EQU)

• Test when two values are equal.• Instruction is true when source A is equal to

source B.

An Equal Instruction Controlling OTE Instruction

Not Equal Instruction (NEQ)

• Test when two values for inequality.• Use this instruction to determine if two

specified sources are not equal.• Instruction is true when source A is not equal

to source B.

Not Equal Instruction

Less Than Instruction (LES) (1 of 2)

• Test when one value is less than another.• Instruction is true when the data stored in

source A is less than either the data stored in the address specified as source B or a constant entered in source B.

The Less Than Instruction (2 of 2)

Less Than or Equal (LEQ)

• Determine if one source of data is less than or equal to another.

• Instruction is true when the data stored in source A is less than or equal to either the data stored in the address specified as source B or a constant entered in source B.

Less Than or Equal Instruction

Greater Than Instruction (GEQ)

• Determine if one source of data is greater than another.

• Instruction is true when the data stored in source A is greater than either the data stored in the address specified as source B or a constant entered in source B.

The Greater Than Instruction

Greater Than or Equal (GEQ)

• Determine if one source of data is greater than or equal to another.

• Instruction is true when the data stored in source A is greater than or equal to either the data stored in the address specified as source B or a constant entered in source B.

Greater Than or Equal Instruction

Data-handling Instructions

• Used when data needs to be moved or copied from one data file source to another

• When data needs to be converted to a different radix

Move Instruction (MOV) (1 of 2)

• This is an output instruction that moves a copy of one data file element to a specified destination.

• The source can be an address or constant.• When instruction is true, a copy of the source

data will be moved to the specified destination address.

Move Instruction (2 of 2)

Masked Move Instruction (MVM) (1 of 2)

• This is an output instruction that moves a copy of one data file element through a mask to a specified destination.

• When true, a copy of the data specified in the source is moved through a hexadecimal mask to the specified destination.

Masked Move Instruction (2 of 2)

Hexadecimal Masking

• Source data is passed through the mask bit by bit.

• Mask bit in same position as source bit determines if data is to pass or not.

• To pass data through mask, set appropriate mask bit.

• To mask data from passing, reset the appropriate mask bit.

Source Data Moved through the Mask to the Destination

Mask Rules

• Mask is either a hexadecimal value or the address where the mask will be found.

• Data is evaluated on a bit by bit basis.• Mask 1 bits allow data to pass.• Mask 0 bits hold data from passing.• Destination bits that correspond to zeros in

the mask are not changed.

FRD Instruction Converting BCD Input Data to Integer

TOD Instruction ConvertingInteger Output Data to BCD

Copy File Instruction (COP)

• Output instruction that copies a user-defined group of 16-bit data file words

• Must copy consecutive dat file elements• Copy up to 128 one-word elements• Source and destination can be different file

types

Copy File Programming Parameters (1 of 2)

• Source is the address of the file to be copied. • The # symbol in front of the source address

specifies this address as the beginning of a user-defined source file.

• Destination is the starting address from which the number of source elements specified in the length parameter will be copied.

• # specifies copying a user-defined file.

Copy File Programming Parameters (2 of 2)

• Length parameter is the number of consecutive elements to be copied.

• Because different file types can be copied, the destination file type and length specify how many elements will be transferred.

Example of Copy File Instruction Operation

Ladder Containing Copy Instruction

AND Instruction

• The AND instruction performs a logical AND operation on two 16-bit words.

OR Instruction on a Ladder Rung

Exclusive-OR Instruction on a Ladder Rung

Not Logic As an Output Instruction on a PLC Ladder Rung

The Limit Test Instruction Testing for Values between 0 and 1750

The Limit Test Instruction Testing for Values outside the Range of 0 to 100

Data Flow from a VFD into the PLC

Scale with Parameters