PM0237 datasheet(22/88 Pages) STMICROELECTRONICS

22 / 88 page

Bluetooth low energy technology

PM0237

22/88

DocID027104 Rev 2

1.8

Generic attribute profile (GATT)

The Generic Attribute Profile (GATT) defines a framework for using the ATT protocol, and it

is used for services, characteristics, descriptors discovery, characteristics reading, writing,

indication and notification.

On GATT context, when two devices are connected, there are two devices roles:

•

GATT client: it is the device which accesses data on the remote GATT server via read,

write, notify, or indicate operations.

•

GATT server: it is the device which stores data locally and provides data access

methods to a remote GATT client.

It is possible for a device to be a GATT server and a GATT client at the same time.

The GATT role of a device is logically separated from the master, slave role. The master,

slave roles define how the BLE radio connection is managed, and the GATT client/server

roles are determined by the data storage and flow of data.

As consequence, it is not required that a slave (peripheral) device has to be the GATT

server and that a master (central) device has to be the GATT client.

Attributes, as transported by the ATT, are encapsulated within the following fundamental

types:

Characteristics (with related descriptors)

Services (primary, secondary and include)

1.8.1

Characteristic attribute type

A characteristic is an attribute type which contains a single value and any number of

descriptors describing the characteristic value that may make it understandable by the user.

A characteristic exposes the type of data that the value represents, if the value can be read

or written, how to configure the value to be indicated or notified, and it says what a value

means.

A characteristic has the following components:

Characteristic declaration

Characteristic value

Characteristic descriptor(s)

PM0237 Datenblatt(PDF) 22 Page - STMicroelectronics