AD1845 Power Supplies
35 & 36
41 & 42
Analog Supply Voltage (+5 V).
34 & 37
40 & 43
1, 7, 15, 19, 45, 54
10, 14, 55, 68, 88, 98
Digital Supply Voltage (+5 V).
2, 8, 16, 20, 25, 44, 53, 64
11, 15, 20, 54, 67, 79, 89, 99
(Continued from page 1) AD1845
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.
B U S
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 suspended independently allowing the AD1845 to be used for capture-only or playback-only, lessening power consumption and extending battery life.
I S A
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”. Additionally, ∑∆ 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.
Figure 1. Interface to ISA Bus
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.
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.
The codec includes a stereo pair of ∑∆ analog-to-digital converters 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-controlled 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 auxiliary line #2 (AUX2) signals to be mixed with the DACs’ output. The ADCs’ output can be digitally mixed with the DACs’ input.
The additional MODE2 functions are: 1. Full-Duplex DMA support. 2. MIC input mixer, mute and volume control. 3. Mono output with mute control.
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, 8-bit unsigned magnitude PCM linear data, and 8-bit µ-law or A-law companded digital data.
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. 7. Capture/Playback FIFO enable/disable.