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# ZED Link Mono GPIO Triggering

The ZED Link Mono [GMSL2](/docs/products/embedded/zed-link-capture-card/gmsl2#what-is-gmsl2) capture card allows you to synchronize external sensors by using triggering signals on the 6-pin 2mm pitch GPIO connector **J4**.

![](/_fern-img/12bfc6c75ef72953c4403791717635bb9b8408f04bbc564ea63de6ff2e992910.webp)![](/_fern-img/6e9b6d9c7582c23ba48ea08bcfe1f9ba46acaf3c74d68e2f129175c52db01167.webp)

## Master mode - Trigger out

The ZED Link Mono capture card is configured to operate in **master mode** by default.

In any case, if you change mode, you can set the card back to master mode by setting `sync_mode=0` in the file `/etc/systemd/system/zed_x_daemon.service` and restarting the ZED X daemon service:

```bash
sudo sed -i 's/^sync_mode=./sync_mode=0/' /etc/systemd/system/zed_x_daemon.service # Set master mode
sudo systemctl daemon-reload # Reload systemd configuration
sudo systemctl restart zed_x_daemon.service # Restart ZED X daemon service
```

The default content of the file `/etc/systemd/system/zed_x_daemon.service` is as follows:

```bash
[Unit]
Description=ZED-X Daemon service
After=nvargus-daemon.service driver_zed_loader.service 
Requires=driver_zed_loader.service
StartLimitIntervalSec=0

[Service]
Type=simple
Restart=always
RestartSec=1
User=root
StandardOutput=syslog
ExecStart=/usr/sbin/ZEDX_Daemon

# 0 = no sync(Default), 1 = master/slave mode, 2 = slave mode only
sync_mode=0 

[Install]
WantedBy=multi-user.target
```

The output synchronization signal is available on **pin #6** of the GPIO connector **J4** as soon as the Jetson™ device boots and the ZED Link [GMSL2](/docs/products/embedded/zed-link-capture-card/gmsl2#what-is-gmsl2) driver is installed.

* Connect the ground signal (Yellow - **GND**) to pin #1.
* Connect the trigger out signal (Green - **MFP0**) to pin #6.

![](/_fern-img/30fda20722f7c88bea26b90444e03cdf46adf7a8c4e1ef3504d0925aff049d99.webp)

### Triggering signal

The output trigger signal is a square wave, with its rising edge synchronized with the end of the exposure phase of the CMOS sensor.

The signal has a fixed **Amplitude** of 3.75V +/- 12%, while **Width** and **Frequency** change according to the frame rate setting of the camera.

#### Frame rate: 120 FPS - ZED X / ZED X Mini / ZED X Nano / ZED X One GS / ZED X One S

* Amplitude: 3.75V +/- 12%
* Width: 2.08 msec
* Frequency: 120 Hz
* Period: 8.33 msec

![](/_fern-files/stereolabs.docs.buildwithfern.com/99f1b9ebac6168656be9252341386194e5056bf0bb6607999d183018dc344db7/docs/products/embedded/zed-link-capture-card/images/zed-link-mono-OSC-120.png)

#### Frame rate: 60 FPS - ZED X / ZED X Mini / ZED X Nano / ZED X One GS / ZED X One S / ZED X One 4K

* Amplitude: 3.75V +/- 12%
* Width: 4.17 msec
* Frequency: 60 Hz
* Period: 16.67 msec

![](/_fern-files/stereolabs.docs.buildwithfern.com/0f9c565fbada2e728dc69f7e6b8f27ba300094d07c2ea37c528b7d015018b640/docs/products/embedded/zed-link-capture-card/images/zed-link-mono-OSC-60.png)

#### Frame rate: 30 FPS - ZED X / ZED X Mini / ZED X Nano / ZED X One GS / ZED X One S / ZED X One 4K

* Amplitude: 3.75V +/- 12%
* Width: 8.33 msec
* Frequency: 30 Hz
* Period: 33.33 msec

![](/_fern-files/stereolabs.docs.buildwithfern.com/31f4440ac4b04854bc6bde78a4f9fa8b2b642fa1bb098cd7d53193c8fe58f5e3/docs/products/embedded/zed-link-capture-card/images/zed-link-mono-OSC-30.png)

#### Frame rate: 15 FPS - ZED X / ZED X Mini / ZED X Nano / ZED X One GS / ZED X One S / ZED X One 4K

* Amplitude: 3.75V +/- 12%
* Width: 16.67 msec
* Frequency: 15 Hz
* Period: 66.67 msec

![](/_fern-files/stereolabs.docs.buildwithfern.com/59404121aaa2d27d2b9b5efd99126208e1df4b081b09e92f3a465c569763d417/docs/products/embedded/zed-link-capture-card/images/zed-link-mono-OSC-15.png)

## Slave mode - Trigger in

The ZED Link Mono capture card requires specific commands to switch to **slave mode**.

1. Set `sync_mode=2` in the file `/etc/systemd/system/zed_x_daemon.service` to enable the external trigger input.

   ```bash
   sudo sed -i 's/^sync_mode=./sync_mode=2/' /etc/systemd/system/zed_x_daemon.service
   ```

2. Reload the systemd configuration:

   ```bash
   sudo systemctl daemon-reload
   ```

3. Connect PIN #1 (`GND`) to the ground signal of the trigger source.

4. Connect PIN #5 (`TRIG_IN - MFP1`) to the trigger input signal, i.e., a 3.3V square wave signal.

5. Restart the driver by restarting the ZED X daemon service:

   ```bash
   sudo systemctl restart zed_x_daemon.service
   ```

To verify that the Slave configuration is active, run the command:

```bash
sudo dmesg | grep Sync
```

The output should be similar to:

```bash
[   XX.XXXXXX] sl_max9296 2-0048: Sync mode configured
```

You must use an external trigger signal with the following characteristics:

* Square wave
* Amplitude: 3.3V +/- 10%
* Frequency: Match the camera grab frame rate setting used with the ZED SDK - 15Hz, 30Hz, 60Hz, or 120Hz

![](/_fern-img/419179dcf35ad06e1d2d256cb8dae1a2cc9b230dd9b20106b0f48474ea2ba64b.webp)

## Master/Slave mode - Multiple ZED Link Mono cards synchronization

When using multiple ZED Link Mono capture cards on the same NVIDIA® Jetson platform (e.g., 2x ZED Link Mono on an NVIDIA® Jetson Orin Nano), it's possible to synchronize them together by using the trigger out signal of one card as the trigger in signal for the other card.

The first [GMSL2](/docs/products/embedded/zed-link-capture-card/gmsl2#what-is-gmsl2) deserializer will automatically be configured as **master**, while the second one will operate in **slave** mode.

1. Set `sync_mode=1` in the file `/etc/systemd/system/zed_x_daemon.service` to enable the master/slave mode.

   ```bash
   sudo sed -i 's/^sync_mode=./sync_mode=1/' /etc/systemd/system/zed_x_daemon.service
   ```

2. Reload the systemd configuration:

   ```bash
   sudo systemctl daemon-reload
   ```

3. Connect together the PIN #1 (`GND`) of both ZED Link Mono cards.

4. Connect the PIN #6 (`TRIG_OUT - MFP0`) of the first card to the trigger input signal PIN #5 (`TRIG_IN - MFP1`) of the second card.

5. Restart the driver by restarting the ZED X daemon service:

   ```bash
   sudo systemctl restart zed_x_daemon.service
   ```