User's Manual

81
www.lairdtech.com
Laird Technologies
BTM510/511
Bluetooth
®
Multimedia Module
Miscellaneous
1. SCO / eSCO Audio Link
BTM modules provide an AT command to establish an SCO/eSCO audio connection between a pair of
BTM modules (or BISM2). This enables the user to create bidirectional audio links independently from a
particular Bluetooth prole. The only prerequisite is the existence of a Rfcomm link (serial port prole)
between the modules. If this link doesn’t exist, it can be created using AT+SPD<BdAddr>. Please refer
to section 2 on page 29.
A SCO/eSCO link is intended for bidirectional transmission of speech. The sampling rate is xed to 8
kHz, meaning a usable bandwidth of 3.5 kHz.
For SCO there are three packet types dened in the Bluetooth specication [1]: HV1, HV2, HV3. Each of
them occupies one slot. They differ in the level of bit error checking. It is recommended to enable all
three packet types for SCO links. This will pass the nal decision down to the baseband. There is no
retransmission of erroneous SCO packets.
For eSCO and basic data rate, there are three packet types dened in the Bluetooth specication [1]: EV3,
EV4, EV5. EV3 occupies one slot, EV4 and EV5 can occupy up to three slots each. They differ in the
level of bit error checking. It is recommended to enable all three packet types for eSCO links. This will
pass the nal decision down to the baseband. eSCO packets involve a CRC code and retransmission
of erroneous eSCO packets.
Packet types and link types (SCO or eSCO) are negotiated on link setup. A BTM can accept either
incoming SCO or eSCO links (S register 584), but not both SCO and eSCO at one time. If the
initiating side requests an unsupported link type, the audio link will fail. The initiating BTM module
is supposed to request the remaining link type in that case.
Table 3.58 lists all AT commands and S-Registers for SCO/eSCO links.
Task AT-Command/S-Register Comment
Initiate SCO link AT+BTAx x = packet type bitmask, recommended value = 7
1 = HV1
2 = HV2
4 = HV3
Initiate eSCO link AT+BTA100x x = packet type bitmask, recommended value = 7
1 = EV3
2 = EV4
4 = EV5
Release SCO/eSCO link AT+BTA0 / AT+BTA
Initiate SCO/eSCO link AT+BTA8 Link type (SCO/eSCO) and packet types dened by
S584.
Enable either SCO or eSCO
for incoming requests and
for AT+BTA8
S584 [0..1] 0 = SCO (HV1,HV2,HV3) enabled
1 = eSCO (EV3,EV4,EV5) enabled
Only one link type can be enabled at one time.
Initiate SCO/eSCO link au-
tomatically on each SPP link
S532 [0..7] The recommended value to enable this feature is
7. Value = bitmask for packet type. The link type
(SCO/eSCO) is dened by S584.
0 : feature disabled
1 : HV1 (S584=0) or EV3 (S584=1)
2 : HV2 (S584=0) or EV4 (S584=1)
4 : HV3 (S584=0) or EV5 (S584=1)
Table 3.58: SCO/eSCO AT-commands and S-Registers
AT COMMAND SET
REFERENCE