The external appearance of this device. The values are composed of a category (10-bits) and sub-categories (6-bits).

The value of this characteristic is a UTF-8 string representing the model number assigned by the device vendor. 

The value of this characteristic is a variable-length UTF-8 string representing the serial number for a particular instance of the device.

The value of this characteristic is a UTF-8 string representing the hardware revision for the hardware within the device.

The value of this characteristic is a UTF-8 string representing the firmware revision for the firmware within the device.

 The value of this characteristic is a UTF-8 string representing the name of the manufacturer of the device.            
		

Contains accelerometer measurements for X, Y and Z axes as 3 signed 16 bit values in that order and in little endian format. X, Y and Z values should be divided by 1000.

Determines the frequency with which accelerometer data is reported in milliseconds.

Valid values are 1, 2, 5, 10, 20, 80, 160 and 640.

Contains magnetometer measurements for X, Y and Z axes as 3 signed 16 bit values in that order and in little endian format. 
Data can be read on demand or notified periodically.

Determines the frequency with which magnetometer data is reported in milliseconds.

Valid values are 1, 2, 5, 10, 20, 80, 160 and 640.

Compass bearing in degrees from North.

0 - state unknown
1 - calibration requested
2 - calibration completed OK
3 - calibration completed with error

State of Button A may be read on demand by a connected client or the client may subscribe to notifications of state change. 
3 button states are defined and represented by a simple numeric enumeration:  0 = not pressed, 1 = pressed, 2 = long press.

State of Button B may be read on demand by a connected client or the client may subscribe to notifications of state change. 
3 button states are defined and represented by a simple numeric enumeration:  0 = not pressed, 1 = pressed, 2 = long press.

Contains data relating to zero or more pins. Structured as a variable length array of up to 19 Pin Number / Value pairs. 

Pin Number and Value are each uint8 fields. 

Note however that the micro:bit has a 10 bit ADC and so values are compressed to 8 bits with a loss of resolution.

OPERATIONS:

WRITE: Clients may write values to one or more pins in a single GATT write operation. 
A pin to which a value is to be written must have been configured for output using the Pin IO Configuration characteristic. 
Any attempt to write to a pin which is configured for input will be ignored.

NOTIFY: Notifications will deliver Pin Number / Value pairs for those pins defined as input pins by the Pin IO Configuration characteristic 
and whose value when read differs from the last read of the pin.

READ: A client reading this characteristic will receive Pin Number / Value pairs for all those pins defined as input pins by the Pin IO Configuration characteristic.

A bit mask which allows each pin to be configured for analogue or digital use.

Bit n corresponds to pin n where 0 LESS THAN OR EQUAL TO n LESS THAN 19. A value of 0 means digital and 1 means analogue.

A bit mask (32 bit) which defines which inputs will be read. If the Pin AD Configuration bit mask is also set the pin will be read as an analogue input, if not it will be read as a digital input.  

Note that in practice, setting a pin's mask bit means that it will be read by the micro:bit runtime and, if notifications have been enabled on the Pin Data characteristic, data read will be transmitted to the connected Bluetooth peer device in a Pin Data notification. If the pin's bit is clear, it  simply means that it will not be read by the micro:bit runtime.

Bit n corresponds to pin n where 0 LESS THAN OR EQUAL TO n LESS THAN 19. A value of 0 means configured for output and 1 means configured for input.

A variable length array 1 to 2 instances of :

struct PwmControlData
 {
 uint8_t     pin;
 uint16_t    value;
 uint32_t    period;
}

Period is in microseconds and is an unsigned int but transmitted.
Value is in the range 0 – 1024, per the current DAL API (e.g. setAnalogValue). 0 means OFF.

Fields are transmitted over the air in Little Endian format.

Allows the state of any|all LEDs in the 5x5 grid to be set to on or off with a single GATT operation. 
Consists of an array of 5 x utf8 octets, each representing one row of 5 LEDs.  
Octet 0 represents the first row of LEDs i.e. the top row when the micro:bit is viewed with the edge connector at the bottom and USB connector at the top. 
Octet 1 represents the second row and so on.
In each octet, bit 4 corresponds to the first LED in the row, bit 3 the second and so on. 
Bit values represent the state of the related LED: off (0) or on (1).

So we have:

Octet 0, LED Row 1: bit4 bit3 bit2 bit1 bit0
Octet 1, LED Row 2: bit4 bit3 bit2 bit1 bit0
Octet 2, LED Row 3: bit4 bit3 bit2 bit1 bit0
Octet 3, LED Row 4: bit4 bit3 bit2 bit1 bit0
Octet 4, LED Row 5: bit4 bit3 bit2 bit1 bit0

A short UTF-8 string to be shown on the LED display. Maximum length 20 octets.

Specifies a millisecond delay to wait for in between showing each character on the display.

A variable length list of event data structures which indicates the types of client event, potentially with a specific value which the micro:bit wishes
to be informed of when they occur. The client should read this characteristic when it first connects to the micro:bit. It may also subscribe to notifications
to that it can be informed if the value of this characteristic is changed by the micro:bit firmware.

struct event {
  uint16 event_type;
  uint16 event_value;
};


Note that an event_type of zero means ANY event type and an event_value part set to zero means ANY event value.

event_type and event_value are each encoded in little endian format.

Contains one or more event structures which should be notified to the client. It supports notifications and as such the client should subscribe to 
notifications from this characteristic.

struct event {
  uint16 event_type;
  uint16 event_value;
};

a variable length list of event data structures which indicates the types of micro:bit event, potentially with a specific value which the client wishes
to be informed of when they occur. The client should write to this characteristic when it first connects to the micro:bit.

struct event {
  uint16 event_type;
  uint16 event_value;
};


Note that an event_type of zero means ANY event type and an event_value part set to zero means ANY event value.

event_type and event_value are each encoded in little endian format.

a writable characteristic which the client may write one or more event structures to, to inform the micro:bit of events which have occurred on the client. 
These should be of types indicated in the micro:bit Requirements characteristic bit mask.

struct event {
  uint16 event_type;
  uint16 event_value;
};

Writing 0x01 initiates rebooting the micro:bit into the Nordic Semiconductor bootloader if the DFU Flash Code characteristic has been written
to with the correct secret key. 

Writing 0x02 to this characteristic  means "request flash code".

Signed integer 8 bit value in degrees celsius.

Determines the frequency with which temperature data is updated in milliseconds.

This characteristic allows the micro:bit to transmit a byte array containing an arbitrary number of arbitrary octet values to a connected device. 

The maximum number of bytes which may be transmitted in one PDU is limited to the MTU minus three or 20 octets to be precise.

This characteristic allows a connected client to send a byte array containing an arbitrary number of arbitrary octet values to a connected micro:bit. 

The maximum number of bytes which may be transmitted in one PDU is limited to the MTU minus three or 20 octets to be precise.