User's Manual

3.3.3.1 Definition of Characteristic Access Commands
RN4020 could be configured to act as server and client at the same time. When it
performs dual roles as server and client, two sets of services and characteristics are
known to RN4020. For services that RN4020 acts as server, it is called server
services, where all values and configurations of characteristics are stored locally.
For services that RN4020 acts as client, it is called client services, where all data and
configurations of characteristics are stored remotely in peer device. To address
server services, the first letter of characteristic access commands is “S”; to address
client services, the first letter of characteristic access commands is “C”.
Bluetooth SIG adopted a group of public services specifications, which are the basis
of interoperability between devices. All service and characteristics in the service
have been assigned 16-bit short UUIDs. On the other hand, users are able to define
their own private service and its associated characteristics with 128-bit long UUIDs.
On the other hand, even it is rare; one public characteristic may be used in more
than one service. Furthermore, because addressing 128bit private characteristic
may not be so efficient, RN4020 provides a unique 16bit reference of handle to each
characteristic. Therefore, a characteristic could be addressed either by its UUID or
its handle. To address a characteristic by its UUID, the second letter of characteristic
access commands is “U”; to address a characteristic by its handle, the second letter
of characteristic access commands is “H”.
In addition, the value or configuration of a characteristic could either be read or
write. To read a characteristic, the third letter of characteristic access commands is
“R”; to write a characteristic, the third letter of characteristic access commands is
“W”.
Finally, access to a characteristic may be directed to its value, or its configuration.
Usually, only the client services needs to access the configuration of a characteristic.
If address by handle, this problem has been solved, since value and configuration of
a characteristic have different handles. But if addressing by UUID, a fourth letter “V”
or “C” needs to be added to indicate whether the access request to client service is
for value or configuration of a characteristic.
Before addressing the characteristics, user may want to know accessible
characteristics. Characteristic Access commands group provides two commands, LC
and LS, to list the client services and server services respectively.
3.3.3.2 LC
Command “LC” lists the available client services and their characteristics. Client
services and their characteristics are only available under two conditions:
 An active connection exists