User's Manual

Enhanced Class 1 Bluetooth v2.1 Module
User’s Guide
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CONN-GUIDE-BT740_v0.2
 None
 Display Only
 Display with a Yes/No button
 Keyboard only
This I/O capability exchanges by the two peers going through a pairing procedure so that the optimal user
interaction selects at both ends. For example, if one end admits to keyboard only and the other to Display
only, then the two negotiate that the display end shows the passcode with an appropriate prompt to get
the user at the other end to type in the passcode.
When either has ‘none’ capability, then pairing procedure completes without any MITM protection by both
ends automatically accepting the passcode generated by the pairing algorithm.
14.7.4.1 I/O Capability
The I/O capability of the module is set via S Register 6 (9006 in AT mode) where the value to set is as
follows:
 12 = No I/O capability
 13 = Display with Yes/No
 14 = Keyboard only
 15 = Display Only
When both ends are keyboard only, you can enter a pre-shared 6 digit number.
When both ends are Display Only it is unlikely the two devices have services that are of use to either and
so it could be contrived combination.
14.7.4.2 Outgoing
To initiate a pairing, the host shall submit the command “AT+BTW<bd_addr>” to which it gets an
immediate OK or ERROR response. The host then shall wait for a “PASSKEY? N <bd_addr>” response
to which it shall respond with the command AT+BTK=”passcode” or “AT+BTKY” or “AT+BTKN”
depending on the value of N in the “PASSKEY?” message.
When the pairing procedure completes, the module sends to the host the following asynchronous
response: “PAIR N <bd_addr>”. N is 0 for a successful pairing, 1 for a timeout, and 2 for a generic failure
(for example, mismatching pincode).
As you can see, the host is able to determine if SSP or legacy pairing is in progress because in the
former the challenge message is “PASSKEY?” whereas in the latter it is “PIN ?”
14.7.4.3 Incoming
The module has to be in at least connectable mode for it to participate in a pairing initiated from a SSP
capable peer. The first indication the host may get is that an incoming pairing has initiated is when it
receives the asynchronous response “PASSKEY? N <bd_addr>”. To this, the host responds with the
command AT+BTK=”passcode” or “AT+BTKY” or “AT+BTKN” depending on the value of N in the
“PASSKEY?” message.
When the pairing procedure completes, and for ‘just works’, the module sends to the host the following
asynchronous response: “PAIR N <bd_addr>”. N is 0 for a successful pairing, 1 for a timeout, and 2 for a
generic failure (for example, mismatching pincode).