# How to use digital/trigger ports

Every Presto comes with 4 digital outputs and 4 digital inputs.

A {mod}`.pulsed` sequence can be triggered either from an internal trigger (by default) or from one
of the 4 digital inputs. An instance of {class}`.TriggerSource` class is passed as an argument to
the {meth}`.Pulsed.run` function. For example, a sequence can be triggered by a signal on digital
input 2:

```python
pls.run(period=1.0, repeat_count=1, num_averages=1, trigger=TriggerSource.DigitalIn2)
```

Digital triggers/markers can be output at defined times during a pulsed sequence using
{meth}`.Pulsed.output_digital_marker`. For example, the following code will output five markers of
increasing length every 5 μs on digital output port 1:

```python
length_list = np.linspace(0.5e-6, 2.5e-6, 5)
port = 1  # int or list of ints in [1,4]
T = 0.0
for length in length_list:
   pls.output_digital_marker(T, length, port)
   T += 5e-6
```
Digital markers have an amplitude of 3.3 V (see the signal captured by the oscilloscope connected
to digital output port 1 below) and an output impedance of 50 Ω.

```{image} images/triggers_light.svg
:align: center
:class: only-light
```

```{image} images/triggers_dark.svg
:align: center
:class: only-dark
```