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DigitalOutput

The DigitalOutput circuit provides a tri-state output which can be driven actively high, low or put into a high-impedance state. The output is fully protected against short circuits and overloads, and has diagnostics to verify correct operation. They can be used to send digital signals to external controllers, switch solid state relays, or even drive small LED indicators.

Digital outputs are not intended to drive heavy loads, or inductive loads. See LoadDriver instead.

Protection

Digital outputs have both hardware and firmware measures to protect the outputs against overloads, or short circuits to the ground, 5V or 15V power rails. The hardware limits the amount of current that the digital output will source or sink to approximately 10mA. If the overload condition persists, the firmware will intervene and put the output in a high-impedance state. API function get_status is available for checking if an overload has occurred and reset_status will clear the overload shutdown status and attempt to re-enable the output.

High State Configuration

The output can be operated either as push-pull or open-collector. Both modes drive the output to a low voltage level when the state is set to false. But they behave differently when the output is set to true. In push-pull the output is driven to a high voltage, whereas open-collector puts the output in a high-impedance state.

Open-collector is useful when sending a signal to the input of another electronic device which might be operating at a different voltage level. In this configuration the receiving device should contain its own pull-up resistor to bias the input to a suitable voltage level.

Use push-pull only when you are certain that the device receiving the signal can handle the high voltage level (typically 5V). This mode can also be useful for driving optocouplers, LEDs and solid-state relays.

set_high_mode is used to select between modes. Driven selects push-pull and Floating selects open-collector.

API

Configuration 

void set_high_mode(HighMode mode)

Configures the output level when state is set to true.
mode is an enum with the following possible values;

  • DigitalOutput::HighMode::Driven to actively drive the output to a high level
  • DigitalOutput::highMode::Floating to leave the output in a high-impedance state
DigitalOutput::HighMode get_high_mode()

Gets the configured behavior for when the output is set to true.
See set_high_mode for details of the returned enum.

void set_state(bool value)

Sets the state of the digital output.
true drives the output to a high level (HighMode::Driven) or high-impedance (HighMode::Floating) depending on the selected HighMode (see set_high_mode).
false drives the output low

bool get_state()

Gets the current state of the digital output.
See set_state for details of the states.

void toggle_state()

Toggles the state of the output.
If the state is State::HighZ (high-impedance) it remains unchanged. Otherwise, State::High is flipped to State::Low and visa-versa.

DigitalOutput::Status get_status()

Gets the status of the output.
Returns a Status enum with the following possible values;

  • DigitalOutput::Status::Ok for normal operation
  • DigitalOutput::Status::OverloadShutdown if output has been disabled (changed to State::HighZ) due to an overload condition.
void reset_status()

Resets status.
If the status was previously Status::OverloadShutdown, it will be reset to Status::Ok and the output will be re-enabled. Operation may resume as normal if the condition that triggered the overload condition has since been cleared. Otherwise the overload protection will again be triggered and the status will return to Status::OverloadShutdown.