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Laird Technologies
BTM520/521
Bluetooth
®
Multimedia Plus Module
CONFIGURING
THE BTM520/521
Hardware Unit Control
This section covers S-Registers and AT-Commands that are related to hardware units within the module.
1. Audio Loopback Mode
For testing purposes, an audio loopback mode will be introduced. The stereo audio input signal
is fed through the Kalimba DSP with running SBC codec, and is directed back to the audio stereo
output. Audio Loopback Mode is controlled with the new AT Command “AT+BTL”.
2. Codec Gain
On BC05-MM, analogue input and output gains can be set to one of 23 steps called “Gain Level”.
To each gain level, an overall gain (dBr) is assigned, according to Table 3 3: Gain Table. Gain values
can be specified either as gain level or as overall gain by separate S Registers. Please note that a
pair of such S-Registers always updates the other corresponding S-Register (e.g. S589 – S689
and S590 – S690).
For S689 and S690 the overall gain (dBr) must be entered multiplied by 10. If the input value
doesn’t match a gain table entry, the nearest possible value is set. The actually set value can be
checked by reading back S689/S690. The value of S689/S690 is printed out multiplied by 10 in
order to avoid non integer numbers.
The new command class “AT+G…” is introduced in Bism3 which enables incremental
and decremental gain settings. The increment/decrement command corresponds to one row
up/down in the gain table (Table 3 3). The Gain level registers S589/S689 and S590/S690 are
not affected by increment/decrement commands. Instead, the current gain level is cached
and can be retrieved by “AT+G(I|O)?”. There are 2 further commands to restore the cached
gain level from S589/S590 (“AT+G(I|O)R”) and to save the currently cached gain level
to S589/S590 (“AT+G(I|O)S”).
Table 3-2: Audio Loopback AT-Commands and S-Registers
TASK
AT-COMMAND / SREGISTER
COMMENT
Set audio loopback mode
AT+BTL<Mode>
Mode:
0 = off
1 = on, via PCM
2 = on, via SBC encoder/decoder
Set sampling rate for Audio
Loopback Mode
S419 [0..6], default=6
0 = 8 kHz
1 = 11.025 kHz
2 = 16 kHz
3 = 22.050 kHz
4 = 24 kHz
5 = 32 kHz
6 = 44.1 kHz
