# App Switcher
MAXREFDES178# has a special application switcher bootloader. App-Switcher can load MAX32666, MAX78000-Video and MAX78000-Audio demo firmware using a micro SD card.
**Warning:** The MAXREFDES178# App-Switcher is available from version **v1.1.67** and later. Please update MAX32666, MAX78000-Video and MAX78000-Audio firmware with the FaceID demo with version **v1.1.67** (or later) by following the steps in the “Load Demo Firmware Using MINGW on Windows” section.
**NOTE:** App-Switcher is embedded in the demo firmware. It is not necessary to load App-Switcher binaries separately.
App-Switcher uses **msbl** files to load MAX32666, MAX78000-Video and MAX78000-Audio firmware from a micro SD card. **msbl** files can be found in `build` directory when the build is completed. Alternatively, you can download the latest **.msbl** files from GitHub Release or GitHub Actions.
## Preparing an SD Card
* Format the micro SD card with **FAT32** file system. **Make sure to back up your SD Card content before formatting!**
* Download the latest maxrefdes178_firmware.zip release from:
* https://github.com/MaximIntegratedAI/refdes/releases for stable releases.
* https://github.com/MaximIntegratedAI/refdes/actions/workflows/maxrefdes178.yml for GitHub Action builds.
* Extract zip content to the micro SD card root directory.
App-Switcher SD Card folder structure requirements:
* All demo directories must be in the root directory of the SD card.
* All demo directories must contain these files:
`maxrefdes178_max32666_demo.msbl`
`maxrefdes178_max78000_video_demo.msbl`
`maxrefdes178_max78000_audio_demo.msbl`
## Running App-Switcher
* Turn off the device by pressing the **power button**.
* Insert the micro SD card.
* While pressing **Button X**, press **power button** to turn on the device.
* The device will start in App-Switcher mode.
* If there isn't a valid demo on MAX32666 flash, App-Switcher will start automatically.
## Loading a Demo From an SD Card
* Pressing **Button X** changes the selected demo. The selected demo will be highlighted in Green.
* **Button Y** starts the firmware update procedure for the selected demo.
* First, App-Switcher loads MAX78000-Audio firmware.
* Then, App-Switcher loads MAX78000-Video firmware.
* And last, App-Switcher loads MAX32666 firmware.
* If all three firmware updates are successful, the device will restart with the selected demo.
* If the micro SD card is not inserted, App-Switcher halts and waits for a restart. Press the power button for 12 seconds to turn off the App-Switcher.
* If the demo folder content is invalid (incorrect or missing **msbl** files), App-Switcher returns to the main menu.