User guide

Silicon Labs Page of 14 21

3.3.3 <value> : Characteristic Value Definition element

The XML element is used to define a characteristic value description.

<value>

The attributes are described in more detail in the table below.

Attribute Description

length

This atttribute defines the fixed length of an attribute or the maximum length of an attribute

if the attribute (see below) is used.

variable_length

Range:

0 - 255 (Bytes)

variable_length

This attribute defines that the length of an attribute is variable.

Range:

0 - 255 (Bytes)

type

This attribute defines how to interpret the element value.

Options:

hex: Value is hex

utf-8: Value is string

user: When this property is used in a characteristic and a remote device tries to read the

value (with ATT read operation), an event is generated to the

User Read Request

application (via BGscript or BGAPI). The application must then provide the attributes value

or an error code to the remote device with the command . This

User Read Response

feature enables the application to dynamically generate the attributes value whenever it's

being requested by a remote device.

The user property can also be used with attributes that can be written. When a remote

device writes an attribute with the user property an event is generated

Attribute Value

where the reason code is The

attributes_attribute_change_reason_write_request_user.

application must then accept or reject the write to the remote device with

User Write

command.

Response

Default:

utf-8: Value is string

Example: A simple characteristic value length definition (20 bytes) and UTF-8 type (since it's the default).

Example: A variable length characteristic definition, where length can be from 0 up to 20 bytes.

Example: Characteristic type definition.

Example: A characteristic type and length definition.

<value length="20" />type="hex"

Example: A characteristic length and user type property definitions.

<value length="20" />type="user"