Configure the Slave unit as follows:
AT&F*
Restore system defaults
ATZ
Reset the unit
ATS512=4 Make
connectable and discoverable
ATS0=1
Answer after 1 ring
ATS531=1
Keep AT command mode going after a connection is
established
ATS589=7
Set Max. Volume level (requires firmware V9_20_22)
AT&W
Save the above settings
ATZ
Reset the unit.
5) Find out the
Bluetooth
address of the Slave Unit by typing ATI4<return>
6) Configure the Master Unit as follows:
AT&F*
Restore System Defaults
ATZ
Reset the unit
ATS531=1
Keep the AT commands going after a connection is
established
ATS589=7
Set volume to maximum
AT&W
Save to flash
ATZ
Reset the unit.
ATD008098nnnnnn
Connect to the slave (substitute your slave’s
Bluetooth
address that you found in step 5 for nnnnnn)
AT+BTA1
Establish an audio link – displays AUDIO ON on both sides.
(Alternatively AT+BTA7 can be used and the units will
negotiate the best link type.)
An Audio link is now established between the two units.
AT=BTA0 will turn off the audio link (but still leave the units connected).
To change volume use ATS589. ATS589=0 gives minimum, ATS589=7 gives maximum.
4.
Bluetooth SCO Links – A Primer
4.1
Normal SCO
Bluetooth
uses a Synchronous Connection-Orientated link (SCO) for audio. All this means is
that for an audio link, the bandwidth needed to maintain the data rates required by the audio
link is pre-allocated between the master and slave. This ensures audio data is always
transmitted at the required data rate, and takes
priority over the transmission
of digital
data.
The
Bluetooth
specification for SCO is such that there is no re-transmission if data is
corrupted or lost. This explains the crackling and popping that occurs when you get to the
limits of radio range.
The actual data rate over the air is 64 kbits/sec. There are 1600 timeslots available per
second and when a master transmits a SCO packet in one timeslot, the slave replies with its
SCO packet in the next. The SCO packet size is fixed at 240 bits (30 bytes). This means
when a SCO link is established using the HV3 packet type, two out of every 6 timeslots are
used up by the SCO link. This means there is enough bandwidth to have up to three SCO
links active between a master and slave at the same time. In this scenario, there are no
spare timeslots for other data.
There are 3 main types of SCO packets, HV1, HV2 and HV3 (High Quality Voice). As
mentioned earlier, the HV3 packet type has a 1 to 1 mapping between incoming audio data
and the data transmitted over the air. There is no error correction possible with HV3.
APN_06002_1v03 Winbond Audio Board Application Note
5