Discrete 2-State Device (D2SD)

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.

The Discrete 2-State Device (D2SD) instruction controls a discrete device which has only two possible states (such as on/off or open/closed).

Available Languages

Ladder Diagram

This instruction is not available in ladder diagram logic.

Function Block

Structured Text

D2SD(D2SD_tag)

Operands

There are data conversion rules for mixed data types within an instruction. See Data Conversion
.

Structured Text

Operand	Type	Format	Description
D2SD tag	DISCRETE_2STATE	Structure	D2SD structure

See Structured Text Syntax
for more information on the syntax of expressions within structured text.

Function Block

Operand	Type	Format	Description
D2SD tag	DISCRETE_2STATE	Structure	D2SD structure

DISCRETE_2STATE Structure

Input Parameter	Data Type	Description
EnableIn	BOOL	Enable input. If false, the instruction does not execute and outputs are not updated. Default is true.
ProgCommand	BOOL	Used to determine CommandStatus when the device is in Program control. When true, the device is commanded to the 1 state; when false, the device is commanded to the 0 state. Default is false.
Oper0Req	BOOL	Operator state 0 request. Set by the operator interface to place the device in the 0 state when the device is in Operator control. Default is false.
Oper1Req	BOOL	Operator state 1 request. Set by the operator interface to place the device in the 1 state when the device is in Operator control. Default is false.
State0Perm	BOOL	State 0 permissive. Unless in Hand or Override mode, this input must be set for the device to enter the 0 state. This input has no effect for a device already in the 0 state. Default is true.
State1Perm	BOOL	State 1 permissive. Unless in the Hand or Override mode, this input must be set for the device to enter the 1 state. This input has no effect for a device already in the 1 state. Default is true.
FB0	BOOL	The first feedback input available to the D2SD instruction. Default is false.
FB1	BOOL	The second feedback input available to the D2SD instruction. Default is false.
HandFB	BOOL	Hand feedback input. This input is from a field hand/off/auto station and it shows the requested state of the field device. When true, the field device is being requested to enter the 1 state; when false, the field device is being requested to enter the 0 state. Default is false.
FaultTime	REAL	Fault time value. Configure the value in seconds of the time to allow the device to reach a newly commanded state. Set FaultTime = 0 to disable the fault timer. If this value is invalid, the instruction assumes a value of zero and sets the appropriate bit in Status. Valid = any float 0.0 Default = 0.0
FaultAlarmLatch	BOOL	Fault alarm latch input. When true and FaultAlarm is true, latch FaultAlarm. To unlatch FaultAlarm set FaultAlmUnlatch to true or clear FaultAlarmLatch to false. Default is false.
FaultAlmUnLatch	BOOL	Fault alarm unlatch input. Set FaultAlmUnLatch when FaultAlarmLatch is set to unlatch FaultAlarm. The instruction clears this input to false. Default is false.
OverrideOnInit	BOOL	Override on initialization request. If this bit is true, then during instruction first scan, the 2-state device is placed in Operator control, Override is set to true, and Hand is cleared to false. If ProgHandReq is true, then Override is cleared to false and Hand is set to true. Default is false.
OverrideOnFault	BOOL	Override on fault request. Set OverrideOnFault to true if the device should go to Override mode and enter the OverrideState on a fault alarm. After the fault alarm is removed, the 2-state device is placed in Operator control. Default is false.
OutReverse	BOOL	Reverse default out state. The default state of Out is cleared to false when commanded to state 0, and set to true when commanded to state 1. When OutReverse is true, Out is set to true when commanded to state 0, and cleared to false when commanded to state 1. Default is false.
OverrideState	BOOL	Override state input. Configure this value to specify the state of the device when the device is in Override mode. True indicates the device should go to the 1 state; false indicates the device should go to the 0 state. Default is false.
FB0State0	BOOL	Feedback 0 state 0 input. Configure the state of the FB0 when the device is in the 0 state. Default is false.
FB0State1	BOOL	Feedback 0 state 1 input. Configure the state of the FB0 when the device is in the 1 state. Default is false.
FB1State0	BOOL	Feedback 1 state 0 input. Configure the state of the FB1 when the device is in the 0 state. Default is false.
FB1State1	BOOL	Feedback 1 state 1 input. Configure the state of the FB1 when the device is in the 1 state. Default is false.
ProgProgReq	BOOL	Program program request. Set to true by the user program to request Program control. Ignored if ProgOperReq is true. Holding this true and ProgOperReq false locks the instruction into Program control. Default is false.
ProgOperReq	BOOL	Program operator request. Set to true by the user program to request Operator control. Holding this true locks the instruction into Operator control. Default is false.
ProgOverrideReq	BOOL	Program override request. Set to true by the user program to request the device to enter Override mode. Ignored if ProgHandReq is true. Default is false.
ProgHandReq	BOOL	Program hand request. Set to true by the user program to request the device to enter Hand mode. Default is false.
OperProgReq	BOOL	Operator program request. Set to true by the operator interface to request Program control. The instruction clears this input to false. Default is false.
OperOperReq	BOOL	Operator operator request. Set to true by the operator interface to request Operator control. The instruction clears this input to false. Default is false.
ProgValueReset	BOOL	Reset program control values. When true, all the program request inputs are cleared to false at each execution of the instruction. Default is false.

Output Parameter	Data Type	Description
EnableOut	BOOL	Indicates if instruction is enabled.
Out	BOOL	The output of the 2-state instruction.
Device0State	BOOL	Device 0 state output. Set to true when the device is commanded to the 0 state and the feedbacks indicate the device really is in the 0 state.
Device1State	BOOL	Device 1 state output. Set to true when the device is commanded to the 1 state and the feedbacks indicate the device really is in the 1 state.
CommandStatus	BOOL	Command status output. Set to true when the device is being commanded to the 1 state and cleared when the device is being commanded to the 0 state.
FaultAlarm	BOOL	Fault alarm output. Set to true if the device was commanded to a new state and the FaultTime has expired without the feedbacks indicating that the new state has actually been reached. Also set to true if, after reaching a commanded state, the feedbacks suddenly indicate that the device is no longer in the commanded state.
ModeAlarm	BOOL	Mode alarm output. Set to true if the device is in Operator control and a program command changes to a state which is different from the state currently commanded by the operator. This alarm is intended as a reminder that a device was left in Operator control.
ProgOper	BOOL	Program/Operator control indicator. True when in Program control. False when in Operator control.
Override	BOOL	Override mode. True when the device is in the Override mode.
Hand	BOOL	Hand mode. True when the device is in the Hand mode.
Status	DINT	Status of the function block.
InstructFault (Status.0)	BOOL	The instruction detected one of the following execution errors. This is not a minor or major controller error. Check the remaining status bits to determine what occurred.
FaultTimeInv (Status.1)	BOOL	Invalid FaultTime value. The instruction sets FaultTime = 0.
OperReqInv (Status.2)	BOOL	Both operator state request bits are true.

Description

The D2SD instruction controls a discrete device which has only two possible states (such as on/off or open/closed). Typical discrete devices of this nature include motors, pumps, and solenoid valves.

Monitoring the D2SD Instruction

There is an operator faceplate available for the D2SD instruction.

Affects Math Status Flags

Major/Minor Faults

None specific to this instruction. See Common Attributes
for operand-related faults.

Execution

Function Block

Condition/State	Action Taken
Prescan	EnableIn and EnableOut bits are cleared to false.
Tag.EnableIn is false	EnableIn and EnableOut bits are cleared to false.
Tag.EnableIn is true	EnableIn and EnableOut bits are set to true. The instruction executes.
Instruction first run	Set ProgOper to Operator Mode. Set CommandStatus to False.
Instruction first scan	Set EnableOut to true. ModeAlarm and operator request inputs are cleared to false, If ProgValueReset is true, all the program request inputs are cleared to false. When OverrideOnInit is true, ProgOper is cleared to false (Operator control). If ProgHandReq is cleared and OverrideOnInit is set, clear Hand and set Override (Override mode). If ProgHandReq is set, set Hand and clear Override (Hand mode).
Postscan	EnableIn and EnableOut bits are cleared to false.

Structured Text

In Structured Text, EnableIn is always true during normal scan. Therefore, if the instruction is in the control path activated by the logic it will execute.

Condition/State	Action Taken
Prescan	See Prescan in the Function Block table.
Normal Execution	See Tag.EnableIn is true in the Function Block table.
Postscan	See Postscan in the Function Block table.

Examples

SD instruction is typically used to control on-off or open-close devices such as pumps or solenoid valves. In this example, the D2SD instruction controls a solenoid valve adding corn syrup to a batch tank. As long as the D2SD instruction is in Program control, the valve opens when the AddSyrup input is set. The operator can also take Operator control of the valve to open or close it if necessary The solenoid valve in this example has limit switches that indicate when the valve is fully closed or opened. These switches are wired into the FB0 and FB1 feedback inputs. This allows the D2SD instruction to generate a FaultAlarm if the solenoid valve does not reach the commanded state within the configured FaultTime.

Function Block

Structured Text

SyrupController.ProgCommand := AddSyrup;

SyrupController.FB0 := SyrupValveClosedLimitSwitch;

SyrupController.FB1 := SyrupValveOpenedLimitSwitch;

D2SD(SyrupController);

SyrupValve := SyrupController.Out;

Switch Between Program Control and Operator Control

The following diagram shows how the D2SD instruction changes between Program control and Operator control.

(1) The instruction remains in Operator control mode when ProgOperReq is true.

Commanded State in Program Control

The following diagram shows how the D2SD instruction operates when in Program control.

Commanded State in Operator Control

The following diagram shows how the D2SD instruction operates when in Operator control.

If both Oper0Req and Oper1Req are true:

The instruction sets the appropriate bit in Status to true

If Override and Hand are false, the instruction holds the previous state.

After every instruction execution, the instruction:

Clears all the operator request inputs to false

If ProgValueReset is true, clears all the program request inputs to false

Hand Mode or Override Mode

The following table describes how the D2SD instruction determines whether to operate in Hand or Override mode.

ProgHandReq	ProgOverrideReq	FaultAlarm and OverrideOnFault	Description
true	either	either	Hand mode Hand is set to true Override is cleared to false
false	true	either	Override mode Hand is cleared to false Override is set to true
false	either	true	Override mode Hand is cleared to false Override is set to true

When the instruction is in Override mode, CommandStatus = OverrideState.

When the instruction is in Hand mode, CommandStatus = HandFB.

Output State

The D2SD output state is based on the state of the command status.

CommandStatus	Output State
false	If OutReverse is false, Out is cleared to false If OutReverse is true, Out is set to true
true	If OutReverse is false, Out is set to rue If OutReverse is true, Out is cleared to false
false and FB0 = FB0State0 and FB1 = FB1State0	The fault timer is stopped and cleared to 0 Device0State is set to true
true and FB0 = FB0State1 and FB1 = FB1State1	The fault timer is stopped and cleared to 0 Device1State is set to true

Fault Alarm Conditions

The D2SD instruction checks for these fault alarm conditions.

Fault alarm condition resulting from	Rules
Device state was commanded to change, but the feedback did not indicate that the desired state was actually reached within the FaultTime	Start the fault timer when CommandStatus_n CommandStatus_n-1 Set FaultAlarm when faulttimer is done and FaultTime > 0.0
The device unexpectedly left a state (according to the feedback) without being commanded to	Set FaultAlarm to true when the fault timer is not timing and one of the following conditions is satisfied: CommandStatus is false and Device0State is false CommandStatus is true and Device1State is false

FaultAlarm is cleared to false if one of the following conditions is met:

CommandStatus is false and Device0State is true

CommandStatus is true and Device1State is true

FaultTime

FaultAlarm cannot be cleared to false when FaultAlarmLatch is true, unless FaultAlmUnlatch is true and no fault is present.

Mode Alarm Conditions

The mode alarm reminds an operator that a device has been left in Operator control. The mode alarm only turns on when, in Operator control mode, the program tries to change the state of the device from the operator’s commanded state. The alarm does not turn on if an operator places a device in Operator control mode and changes the state. The D2SD instruction checks for mode alarm conditions, using these rules.

ModeAlarm	When
True	ProgCommand_n ProgCommandn-1 and ProgCommand_n CommandStatus
False	ProgCommand = CommandStatus or the device is in Override, Hand, or Program control mode

Process Control Instructions

Instruction Set

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