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TDA9855

I2C-bus controlled BTSC stereo/SAP decoder and audio processor

Philips Electronics 

Philips Semiconductors

I2C-bus controlled BTSC stereo/SAP

decoder and audio processor

Product specification

TDA9855

SUBWOOFER; SURROUND SOUND CONTROL

The subwoofer or the surround mode can be activated with

the control bit SUR (see Table 6). A low bit provides an

output signal 1⁄2(L + R) in subwoofer mode, a high bit

selects surround mode and provides an output signal

1⁄2(L − R). The signal is fed through a volume control stage

with a range from +14 to −14 dB in 2 dB steps on top of the

main channel control to the output pin OUTS. The last

setting is the mute position (see Table 11). The capacitor

C35 at pin SW provides a 230 Hz low-pass filter in

subwoofer mode. In surround mode this capacitor should

be disconnected. If balance is not in mid position the

selected left and right output levels will be combined.

MUTE

The mute function can be activated independently with the

last step of volume or subwoofer/surround control at the

left, right or centre output. By setting the general mute bit

GMU via the I2C-bus all audio part outputs are muted.

All channels include an independent zero-crossing

detector. The zero-crossing mute feature can be selected

via bit TZCM:

TZCM = 0: forced mute with direct execution

TZCM = 1: execution in time with signal zero-crossing.

In the zero-crossing mode a change of the GMU bit is

activated but not executed. The execution is enabled at

the next zero-crossing of the signal. To avoid a large delay

of mute switching, when very low frequencies are

processed, or the output signal amplitude is lower than the

DC offset voltage, the following I2C-bus transmissions are

needed:

A first transmission for mute execution

A second transmission approximately 100 ms later,

which must switch the zero-crossing mode to forced

mute (TZCM = 0)

A third transmission to reactivate the zero-crossing

mode (TZCM = 1). This transmission can take place

immediately, but must follow before the next mute

execution.

Adjustment procedure

COMPOSITE INPUT LEVEL ADJUSTMENT

Apply the composite signal (from the FM demodulator)

with 100% modulation (25 kHz deviation) L + R;

fi = 300 Hz. Set input level control via the I2C-bus

monitoring line output (500 mV ±20 mV). Store the setting

in a non-volatile memory. Adjustment of the spectral and

wideband expander is performed via the stereo channel

separation adjust.

AUTOMATIC ADJUSTMENT PROCEDURE

• Capacitors of external inputs EIL and EIR must be

grounded

• Composite input signal L = 300 Hz, R = 3.1 kHz,

14% modulation for each channel; volume gain +16 dB

via the I2C-bus; to avoid annoying sound level set GMU

bit to logic 1 during adjustment procedure

• Effects, AVL, loudness off

• Selector setting SC0, SC1 and SC2 = 0, 0, 0

(see Table 12)

• Line out setting bits: STEREO = 1, SAP = 0

(see Table 21)

• Start adjustment by transmission ADJ = 1 in register

ALI3; the decoder will align itself

• After 1 second, stop alignment by transmitting ADJ = 0

in register ALI3 read the alignment data by an I2C-bus

read operation from ALR1 and ALR2

(see Chapter “I2C-bus protocol”) and store it in a

non-volatile memory; the alignment procedure

overwrites the previous data stored in ALI1 and ALI2

• Disconnect the capacitors of external inputs from

ground.

MANUAL ADJUSTMENT

Manual adjustment is necessary when no dual tone

generator is available (e.g. for service).

• Spectral and wideband data have to be set to 10000

(middle position for adjustment range)

• Composite input L = 300 Hz; 14% modulation

• Adjust channel separation by varying wideband data

• Composite input L = 3 kHz; 14% modulation

• Adjust channel separation by varying spectral data

• Iterative spectral/wideband operation for optimum

adjustment

• Store data in non-volatile memory.

After every power-on, the alignment data and the input

level adjustment data must be loaded from the non-volatile

memory.

TIMING CURRENT FOR RELEASE RATE

Due to possible internal and external spreading, the timing

current can be adjusted via the I2C-bus (see Table 25) as

recommended by dbx.

1997 Nov 04

11

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