Latch¶

This chapter describes the Latch interface. It provides an interface to configure and access a latch in a controller, usually a position latch that is triggered by a configurable input.

Behavior¶

A latch stores a value from a DataSource when it is triggered. See figure Latch state machine for the functional diagram of a latch.

Latch state machine¶

A latch must be configured. The DataSource and TriggerSource inputs must be connected to a signal. TriggerType and TriggerMode options must be specified, for which supported options are listed in tables Latch trigger types and Latch trigger modes.

Latch trigger types¶
Trigger type	Description
None	Trigger type not configured
RisingEdge	Trigger on rising edges
FallingEdge	Trigger on falling edges
AnyEdge	Trigger on both falling and rising edges

Latch trigger modes¶
Trigger mode	Description
None	Trigger mode not configured
OneShot	Latch is disabled after first trigger event
Continuous	Latch is re-enabled automatically after a trigger event

IController.Latches
ILatch.TriggerMode
ILatch.TriggerType

C++

IController::GetLatches()
ILatch::SetTriggerMode()
ILatch::SetTriggerType()

See figure Latch state diagram for a state diagram and table Latch states for state descriptions.

Latch state diagram¶

Latch states¶
State	Description
NotConfigured	Latch is not configured. Required configurations are DataSource input, TriggerSource input, latch trigger type and trigger mode.
Configured	Latch is configured.
Waiting	Latch is waiting for trigger event. Modifying the data or trigger source input is not allowed in this state.
Triggered	Latch is triggered.

A latched value does not change when the value of the DataSource signal changes, e.g. due to sensor scaling. Only after the latch is successfully triggered again, the latched value is updated.

Signals¶

Signals present for latches are described in table Latch signals.

Latch signals¶
Signal	Data type	R/W	Description
Value	<latch specific>	R	Latched data source value.

Inputs¶

A latch has inputs as described in table Latch inputs.

Latch inputs¶
Name	Data type	Description
DataSource	<latch specific>	Input for signal to be latched.
TriggerSource	Bool	Input for trigger signal.

Events¶

The latch has the following events:

Triggered (Active when the latch state equals “Triggered”.)