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AD1845

Parallel-Port 16-Bit SoundPort® Stereo Codec

Analog Devices 

Power Supplies

Pin Name

PLCC

VCC

GNDA

35 & 36

34 & 37

VDD

1, 7, 15,

19, 45,

54

GNDD

2, 8, 16,

20, 25,

44, 53,

64

TQFP

I/O

41 & 42

I

40 & 43

I

10, 14,

I

55, 68,

88, 98

11, 15, 20,

I

54, 67,

79, 89,

99

AD1845

Description

Analog Supply Voltage (+5 V).

Analog Ground.

Digital Supply Voltage (+5 V).

Digital Ground.

(Continued from page 1)

AD1845

CS

A1

A0

WR

RD

DATA7:0

DBDIR

DBEN

PDRQ

CDRQ

PDAK

CDAK

INT

ADDRESS

DECODE

18

8

74_245

8

DIR

G

B

A

AEN

SA19:2

SA1

SA0

IOWC

I

IORC

S

A

DATA7:0

B

U

S

DRQ <X>

DRQ <Y>

DAK <X>

DAK <Y>

IRQ <Z>

Figure 1. Interface to ISA Bus

External circuit requirements are limited to a minimal number

of low cost support components. Anti-imaging DAC output

filters are incorporated on-chip. Dynamic range exceeds 80 dB

over the 20 kHz audio band. Sample rates from 4 kHz to 50 kHz

are supported from a single external crystal or clock source.

The AD1845 has built-in 8/16 mA (user selectable) bus drivers.

If 24 mA drive capability is required, the AD1845 generates

enable and direction controls for IC bus buffers such as the

74 245.

The codec includes a stereo pair of ∑∆ analog-to-digital con-

verters and a stereo pair of ∑∆ digital-to-analog converters. The

AD1845 mixer surpasses MPC Level-2 recommendations.

Inputs to the ADC can be selected from four stereo pairs of

analog signals: line (LINE), microphone (MIC), auxiliary line

#1 (AUX1), and post-mixed DAC output. A software-con-

trolled programmable gain stage allows independent gain for

each channel going into the ADC. In addition, the analog mixer

allows the mono input (M_IN), MIC, AUX1, LINE and auxil-

iary line #2 (AUX2) signals to be mixed with the DACs’ output.

The ADCs’ output can be digitally mixed with the DACs’ input.

The pair of 16-bit outputs from the ADCs is available over a

byte-wide bidirectional interface that also supports 16-bit digital

input to the DACs and control information. The AD1845 can

accept and generate 16-bit twos complement PCM linear digital

data in both little endian or big endian byte ordering, 8-bit

unsigned magnitude PCM linear data, and 8-bit µ-law or A-law

companded digital data.

The ∑∆ DACs are preceded by a digital interpolation filter. An

attenuator provides independent user volume control over each

DAC channel. Nyquist images and shaped quantized noise are

removed from the DACs’ analog stereo output by on-chip

switched-capacitor and continuous-time filters.

The AD1845 supports multiple low power and power-down

modes to support notebook and portable computing multimedia

applications. The ADC, DAC, and mixer paths can be sus-

pended independently allowing the AD1845 to be used for

capture-only or playback-only, lessening power consumption

and extending battery life.

The AD1845 includes a variable sample frequency generator,

that allows the codec to instantaneously change sample rates

with a resolution of 1 Hz without “clicks” and “pops.” Addi-

tionally, ∑∆ quantization noise is kept out of the 20 kHz audio

band regardless of the chosen sample rate. The codec uses the

variable sample frequency generator to derive all internal clocks

from a single external crystal or clock source.

Expanded Mode (MODE2)

MODE1 is the initial state of the AD1845. In this state the

AD1845 appears as an AD1848 compatible device. To access

the expanded modes of operation on the AD1845, the MODE2

bit should be set in the Miscellaneous Information Control

Register. When this bit is set to one, 16 additional indirect

registers can be addressed allowing the user to access the

AD1845’s expanded features. The AD1845 can return to

MODE1 operation by clearing the MODE2 bit. In both

MODE1 and MODE2, the capture and playback FIFOs are

active to prevent data loss.

The additional MODE2 functions are:

1. Full-Duplex DMA support.

2. MIC input mixer, mute and volume control.

3. Mono output with mute control.

4. Mono input with mixer volume control.

5. Software controlled advanced power-down modes.

6. Programmable sample rates from 4 kHz to 50 kHz in 1 Hz

increments.

REV. C

–9–

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