User's Manual

Enhanced Class 1 Bluetooth v2.1 Module
User’s Guide
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79
CONN-GUIDE-BT740_v0.2
3
FLOW_IN
??
Runtime value
4
MODE
0..1, 0xFF
0 = Disable,
1 = Generic Access Code
0xFF = Read current mode
Response Packet
Offset
Field
Value
Comments
0
LENGTH
6
Fixed
1
CHANNEL
0
Fixed
2
COMMAND
[CMD_ DISCOVERABLE_MODE]
3
FLOW_OUT
??
Runtime value
4
STATUS
As appropriate
5
CURMODE
0..1
1 = Generic Access Code
The module uses the parameters stored in ‘S’ Registers 7 and 8 to set the inquiry scan interval and
window. Inquiry scan is how often (interval) the radio listens for an inquirer and for how long (window)
each time.
8.15 Pairing Commands
This group of commands manages either incoming or outgoing pairings and the trusted device database
which resides in the non-volatile memory of the module.
The trusted device database is a database with a two tables, each with records of two fields. One field is
the Bluetooth address of a paired device and the other stores the 16 byte link key.
One database is classed a ROLLING database and stores new pairing information as they happen. If the
database is full, then the oldest is discarded to make space for the latest one.
The other database is classed as a PERSISTANT database which stores pairing information which can
ONLY be deleted when a new pairing initiates to that particular device OR on request from the host.
The host protocol provides for a command to transfer a record between these two databases. In addition
there is a command for the host to determine if a device is trusted. There is also a command to manually
insert a device and its link key into the database.
Depending on the peer device, either a legacy pairing procedure or a simple secure pairing occurs. A
legacy pairing occurs if the peer device is older than v2.1 of the Bluetooth specification. Simple Secure
Pairing (for v2.1 and newer devices) uses a Diffie-Hellman procedure to exchange the secret link key, but
is vulnerable to man-in-the-middle attack.
When pairing initiates and a legacy 2.0 or older device is not involved, then the basebands perform an I/O
capability negotiation with each other to see whether it shall perform a ‘Just Works’ unathenticated pairing
with no man-in-the-middle (MITM) protection or an authenticated pairing which requires user interaction.
The I/O capability is one of:
 Display Only
 Keyboard Only
 Display with Yes/No button