SAA7806H NXP [NXP Semiconductors], SAA7806H Datasheet - Page 11

• Manufacturer Part Number: SAA7806H
• Description: One chip automotive CD audio device
• Manufacturer: NXP [NXP Semiconductors]

Philips Semiconductors
9397 750 13697
Objective data sheet
6.3 General purpose analog inputs
6.4 Auxiliary analog inputs
Sys_clk is the primary clock used by the channel decoder and ARM clock generators. This
clock operates at 67 MHz with either an 8 MHz or 16 MHz crystal or resonator. The
divide-by-2 is selected when a 16 MHz crystal or resonator is used.
The two general-purpose ADC inputs (A_IN_1, pin 6 and A_IN_2, pin 7) can be used for
giving the ARM microcontroller access to external analog sources, e.g. for monitoring
temperature and to provide simple resistor-ladder keypad functionality. These inputs use
an additional pair of sigma-delta ADCs identical to those used for the LF diode inputs.
The general purpose analog inputs have separate interrupt request lines and use address
space in the servo registers for storing the converted digital values. The output of the
general-purpose ADCs are low-pass filtered and can have fine offset compensation
added before being passed to a decimation filter. The digital values from the decimation
filter are then captured in the servo registers with 10-bit resolution per channel. See
Figure
Two further analog inputs, AUX_L and AUX_R, are available with sufficient resolution for
inputting external audio sources, e.g. for allowing ARM access to an external audio source
for sound processing algorithms.
This allows audio processing of external audio sources via the AUX pins, whilst
simultaneously using the general purpose inputs for keyboard and temperature inputs.
Since these two inputs share one pair of the LF sigma-delta ADCs used in the LF path (for
inputs D1 and D2) a multiplexer is used to control the data source into the ADCs. For this
reason, D1 and D2 cannot be used at the same time as AUX_IN_L and AUX_IN_R. A
further multiplexer is used to switch the input pads from the headphone input buffer modes
Fig 6. General purpose analog inputs block diagram
6.
A_IN_1
A_IN_2
or
6 or 7
Rev. 01 — 20 June 2005
reg 2F8 for A_IN_1
reg 2FC for A_IN_2
COMPENSATION
SIGMA-DELTA
DC OFFSET
ADC
GENERATOR
INTERRUPT
LOW-PASS
One chip automotive CD audio device
FILTER
IRQ
to ARM microprocessor
reg 318 for A_IN_1
reg 31C for A_IN_2
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
FINE DC OFFSET
COMPENSATION
DECIMATION
REGISTERS
(10-BIT)
FILTER
SERVO
001aab750
SAA7806
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