The format field determines how a single value contained in the Characteristic Value is formatted.

The information contained on this page is referenced in Bluetooth® Core Specification Volume 3, Part G, Section 3.3.3.5.2.

If a format is not a whole number of octets, then the data shall be contained within the least significant bits of the value, and all other bits shall be set to zero on transmission and ignored upon receipt. If the Characteristic Value is less than an octet, it occupies an entire octet. The following format values are defined:

Format Short Name Description Exponent Value
0x00 rfu Reserved for future use No
0x01 boolean unsigned 1-bit; 0=false, 1=true No
0x02 2bit unsigned 2-bit integer No
0x03 nibble unsigned 4-bit integer No
0x04 uint8 unsigned 8-bit integer Yes
​0x05 uint12 unsigned 12-bit integer Yes
​0x06 uint16 unsigned 16-bit integer Yes
0x07 uint24 unsigned 24-bit integer Yes
​0x08 uint32 unsigned 32-bit integer Yes
​0x09 uint48 unsigned 48-bit integer Yes
​0x0A uint64 unsigned 64-bit integer Yes
​0x0B uint128 unsigned 128-bit integer Yes
​0x0C sint8 signed 8-bit integer Yes
​0x0D sint12 signed 12-bit integer Yes
​0x0E sint16 signed 16-bit integer Yes
​0x0F sint24 signed 24-bit integer Yes
​0x10 sint32 signed 32-bit integer Yes
​0x11 sint48 signed 48-bit integer Yes
​0x12 sint64 signed 64-bit integer Yes
​0x13 sint128 signed 128-bit integer Yes
​0x14 float32 IEEE-754 32-bit floating point No
​0x15 float64 IEEE-754 64-bit floating point No
​0x16 SFLOAT IEEE-11073 16-bit SFLOAT No
​​0x17 FLOAT IEEE-11073 32-bit FLOAT No
​​0x18 duint16 IEEE-20601 format No
​​0x19 utf8s UTF-8 string No
​0x1A utf16s UTF-16 string No
​​0x1B struct Opaque structure No
​​0x1C-0xFF rfu Reserved for Future Use No

Additional Formatting Notes

  • When encoding an IPv4 address, the uint32 Format type shall be used.
  • When encoding an IPv6 address, the uint128 Format type shall be used.
  • When encoding a Bluetooth BD_ADDR, the uint48 Format type shall be used.
  • A duint16 is two uint16 values concatenated together.