3.5.4
Bank-Switch Timeline
3.5.5
Bank-Switching Example 1
3.5.6
Bank-Switching Example 2
TAS5508B
8-Channel Digital Audio PWM Processor
www.ti.com
SLES162C – DECEMBER 2005 – REVISED JULY 2009
After a bank switch is initiated (manual or automatic), no I2C writes to the TAS5508B should occur before
a minimum of 186 ms. This value is determined by the volume ramp rates for a particular sample rate.
Problem: The audio unit containing a TAS5508B needs to handle different audio formats with different
sample rates. Format #1 requires fS = 32 kHz, format #2 requires fS = 44.1 kHz, and format #3 requires fS
= 48 kHz. The sample-rate-dependent parameters in the TAS5508B require different coefficients and data
depending on the sample rate.
Strategy: Use the TAS5508B bank-switching feature to allow for managing and switching three banks
associated with the three sample rates, 32 kHz (bank 1), 44.1 kHz (bank 2), and 48 kHz (bank 3).
One possible algorithm is to generate, load, and automatically manage bank switching for this problem:
1. Generate bank-related coefficients for sample rates of 32 kHz, 44.1 kHz, and 48 kHz, and include the
same in the microprocessor-based TAS5508B I2C firmware.
2. On TAS5508B power up or reset, the microprocessor runs the following TAS5508B initialization code:
a.
Update bank 1 (write 0x0004 8040 to register 0x40).
b.
Write bank-related I2C registers with appropriate values for bank 1.
c.
Write bank 2 (write 0x0005 8040 to register 0x40).
d.
Load bank-related I2C registers with appropriate values for bank 2.
e.
Write bank 3 (write 0x0006 8040 to register 0x40).
f.
Load bank-related I2C registers with appropriate values for bank 3.
g.
Select automatic bank switching (write 0x0003 8040 to register 0x40).
3. When the audio media changes, the TAS5508B automatically detects the incoming sample rate and
automatically switches to the appropriate bank.
In this example, any sample rates other than 32 kHz and 44.1 kHz use bank 3. If other sample rates are
used, then the banks must be set up differently.
Problem: The audio system uses all of the sample rates supported by the TAS5508B. How can the
automatic bank switching be set up to handle this situation?
Strategy: Use the TAS5508B bank-switching feature to allow for managing and switching three banks
associated with sample rates as follows:
Bank 1: Coefficients for 32 kHz, 38 kHz, 44.1 kHz, and 48 kHz
Bank 2: Coefficients for 88.2 kHz and 96 kHz
Bank 3: Coefficients for 176.4 kHz and 192 kHz
One possible algorithm is to generate, load, and automatically manage bank switching for this problem:
1. Generate bank-related coefficients for sample rates 48 kHz (bank 1), 96 kHz (bank 2), and 192 kHz
(bank 3) and include the same in the microprocessor-based TAS5508B I2C firmware.
2. On TAS5508B power up or reset, the microprocessor runs the following TAS5508B initialization code:
a.
Update bank 1 (write 0x0004 F00C to register 0x40).
b.
Write bank-related I2C registers with appropriate values for bank 1.
c.
Write bank 2 (write 0x0005 F00C to register 0x40).
d.
Load bank-related I2C registers with appropriate values for bank 2.
e.
Write bank 3 (write 0x0006 F00C to register 0x40).
f.
Load bank-related I2C registers with appropriate values for bank 3.
g.
Select automatic bank switching (write 0x0003 F00C to register 0x40).
3. When the audio media changes, the TAS5508B automatically detects the incoming sample rate and
automatically switches to the appropriate bank.
TAS5508B Controls and Status
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