Laird BT740 Series, Быстрый старт

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BT740 Development Kit
Quick Start Guide
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23 Laird Technologies
D
IFFERENCE BETWEEN
BT
V
2.0
AND
BT
V
2.1
One of the major differences between Bluetooth v2.0 and Bluetooth v2.1 is the introduction of Simple Secure
Pairing (SSP). SSP simplifies pairing so it doesn’t rely on a pre-shared pin code as it was in BTv2.0. With
BTv2.1, all connections are forced to be encrypted.
SSP uses the Diffie-Hellman public/private encryption methodology to expedite a common 128 bit key at both
ends. This eliminates the need for pre-shared pin codes but introduces the ‘man in the middle’ (MITM) attack
vulnerability. To reduce the possibility of being successfully attacked, a random six-digit passcode is used.
Bluetooth v2.1 devices are required to have I/O capability to ensure that users can interact to the six digit
passcode. One example is mobile phones: they can display the passcode and the user can click Yes to pair.
Bluetooth v2.0 devices require a pre-shared pin code for pairing. Today, there are still many M2M
applications with BT v2.0 connectivity. These M2M devices do not typically have I/O capability, such as a
display or Yes/No options for users to perform pairing. Most importantly, they can be in hard-to-reach places.
On the BT740, the pre-shared pin code can be pre-entered before pairing takes place if it is a BT v2.0 device
the module is attempting to pair with. Further explanation can be found in
Pairing Procedure .
I/O capability
The I/O capability of the module is set via S Register 6 (9006 in AT mode) with the following values:

12(0x0C) = No I/O capability

13(0x0D) = Display with Yes/No

14(0x0E) = Keyboard only

15(0x0F) = Display Only
When both ends are Keyboard only, a pre-shared six digit number can be entered.
When both are Display only, it is unlikely the devices have services that are useful to either. It may be a
contrived combination.
Users should set the module I/O capability value which is suitable to their applications.
Pairing Procedure
Depending on the peer device, either a legacy pairing or a SSP procedure occurs. Table 2 lists combinations:
Table 2: Pairing procedures
Local Device Peer Device Pairing
BTM74X BT 2.1 or later SSP
BTM74X BT 2.0 Legacy pairing
To demonstrate the difference, see the following sections.