Subtract (SUB)
This information applies to the CompactLogix 5370, ControlLogix 5570, Compact GuardLogix 5370, GuardLogix 5570, Compact GuardLogix 5380, CompactLogix 5380, CompactLogix 5480, ControlLogix 5580, and GuardLogix 5580 controllers. Controller differences are noted where applicable.
When enabled, the SUB instruction and the operator '-' subtracts Source B from Source A.
Available Languages
Ladder Diagram
Function Block Diagram
Function Block Diagram supports these elements:
FBD Block
FBD Function
TIP:
FBD Function is applicable to CompactLogix 5380, CompactLogix 5480, ControlLogix 5580, Compact GuardLogix 5380, and GuardLogix 5580 controllers only.
Structured Text
This instruction is not available in structured text.
TIP:
Use the operator '-' in an expression to compute the same result. Refer to Structured Text Syntax for more information on the syntax of expressions and assignments within structured text.
Operands
IMPORTANT:
Unexpected operation may occur if:
- Output tag operands are overwritten.
- Members of a structure operand are overwritten.
- Except when specified, structure operands are shared by multiple instructions.
There are data conversion rules for mixing numeric data types within an instruction. See Data Conversions.
Ladder Diagram
Operand | Data Type CompactLogix 5370, ControlLogix 5570, Compact GuardLogix 5370, and GuardLogix 5570 controllers | Data Type CompactLogix 5380, CompactLogix 5480, ControlLogix 5580, Compact GuardLogix 5380, and GuardLogix 5580 controllers | Format | Description |
|---|---|---|---|---|
Source A | SINT INT DINT REAL | SINT INT DINT LINT USINT UINT UDINT ULINT REAL LREAL LTIME* TIME* TIME32* LDT* DT* | immediate tag | Value from which to subtract Source B. |
Source B | SINT INT DINT REAL | SINT INT DINT LINT USINT UINT UDINT ULINT REAL LREAL LTIME* TIME* TIME32* LDT* DT* | immediate tag | Value to subtract from Source A. |
Dest | SINT INT DINT REAL | SINT INT DINT LINT USINT UINT UDINT ULINT REAL LREAL LTIME* TIME* TIME32* LDT* DT* | tag | Tag to store result of the instruction. |
TIP:
*Keep these considerations in mind when using relative time (LTIME, TIME32, TIME) and absolute time (LDT, DT) data types in SUB instructions:
- If both Source A and Source B are relative time, the Dest must be relative time.
- If Source A is relative time and Source B is absolute time or vice versa, the Dest must be absolute time.
- In ADD instructions, Source A and Source B cannot both be absolute time.
See Time and date data types for a complete description of Relative Time (LTIME, TIME, and TIME32) and Absolute Time (LDT and DT) data types.
Function Block Diagram
FBD Block
Operand | Data Type | Format | Description |
|---|---|---|---|
SUB | FBD_MATH | tag | SUB structure |
FBD_MATH Structure
Input Members | Data Type | Description |
|---|---|---|
EnableIn | BOOL | Enable input. If false, the instruction does not execute and outputs are not updated.
Default is true. |
SourceA | REAL | Value from which to subtract SourceB. |
SourceB | REAL | Value to subtract from SourceA. |
Output Members | Data Type | Description |
|---|---|---|
EnableOut | BOOL | Indicates if the instruction executed without fault when it was enabled. |
Dest | REAL | Result of the instruction. |
FBD Function
TIP:
FBD Function is applicable to CompactLogix 5380, CompactLogix 5480, ControlLogix 5580, Compact GuardLogix 5380, and GuardLogix 5580 controllers only.
Input Operands (Left Pins) | CompactLogix 5380, CompactLogix 5480, ControlLogix 5580, Compact GuardLogix 5380, and GuardLogix 5580 controllers Data Type | Description |
|---|---|---|
SourceA (top) | SINT USINT INT UINT DINT UDINT LINT ULINT REAL LREAL | Value from which to subtract SourceB. |
SourceB (bottom) | SINT USINT INT UINT DINT UDINT LINT ULINT REAL LREAL | Value to subtract from SourceA. |
Output Operand
(Right Pin) | CompactLogix 5380, CompactLogix 5480, ControlLogix 5580, Compact GuardLogix 5380, and GuardLogix 5580 controllers Data Type | Description |
|---|---|---|
Dest | DINT UDINT LINT ULINT REAL LREAL | Result of the function. |
See FBD Functions.
Affects Math Status Flags
Controllers | Affects Math Status Flags |
|---|---|
CompactLogix 5380, CompactLogix 5480, ControlLogix 5580, Compact GuardLogix 5380, and GuardLogix 5580 controllers | Conditional |
CompactLogix 5370, ControlLogix 5570, Compact GuardLogix 5370, and GuardLogix 5570 controllers | Yes |
See Math Status Flags.
Major/Minor Faults
None specific to this instruction. See Index Through Arrays for array-indexing faults.
Execution
Ladder Diagram
Condition/State | Action Taken |
|---|---|
Prescan | N/A |
Rung-condition-in is false | Set Rung-condition-out to Rung-condition-in |
Rung-condition-in is true | Set Rung-condition-out to Rung-condition-in Dest = Source A - Source B |
Postscan | N/A |
Function Block Diagram
FBD Block
Condition/State | Action Taken |
|---|---|
Prescan | N/A |
EnableIn is false | Set EnableOut to EnableIn |
EnableIn is true | Dest = SourceA - SourceB If overflow occurs Clear EnableOut to false else Set EnableOut to true |
Instruction first run | N/A |
Instruction first scan | N/A |
Postscan | N/A |
FBD Function
TIP:
FBD Function is applicable to CompactLogix 5380, CompactLogix 5480, ControlLogix 5580, Compact GuardLogix 5380, and GuardLogix 5580 controllers only.
Condition/State | Action Taken |
|---|---|
Prescan | N/A |
Normal Scan | Dest = SourceA - SourceB |
Instruction first run | N/A |
Instruction first scan | N/A |
Postscan | N/A |
Examples
Ladder Diagram
Function Block Diagram
FBD Block
FBD Function
Structured Text
DINT_dest := DINT_srcA - DINT_srcB;
Provide Feedback