BLEFriend modules can be operated in one of three modes:
Data mode makes use of the BLE UART Service, and turns the BLEFriend into a HW UART bridge between a BLE Central device (your phone or tablet) and your PC or USB-enabled device.
To use data mode, simply connect your BLEFriend module to the USB port on your PC, mode the mode selection switch to UART and start sending or receiving data at 9600 bps using your favorite terminal software.
If the MODE LED blinks twice followed by a three second delay you are in Data Mode:
Command mode is used to send configuration commands to the module or retrieve information about the module itself or the device connected on the other side of the BLE connection.
To use command mode, make sure that the mode selection switch is set to CMD, and enter a valid Hayes AT style command using your favorite terminal emulator at 9600 bps (for example 'ATI' to display some basic info about the module).
If the MODE LED blinks three times followed by a three second delay you are in Command Mode:
For more information on this operating mode see the dedicated Command Mode page in this learning guide.
DFU Mode (which stands for 'device firmware upgrade' or sometimes 'device field update') is a special mode that allows you to update the firmware on the BLEFriend over the air using dedicated DFU applications available on iOS and Android.
This allows you to update your device with the latest BLEFriend firmware from Adafruit without having to purchase an external HW debugger like the Segger J-Link.
To enter DFU mode hold down the DFU button while inserting the BLEFriend into the USB port.
If the LED blinks at a constant rate, you know that you are in DFU mode:
For more information on DFU mode see the dedicate Device Field Update (DFU) page.