UDA1321 datasheet(13/44 Pages) PHILIPS

13 / 44 page

1998 Oct 06

Philips Semiconductors

Preliminary speciﬁcation

Universal Serial Bus (USB)

Digital-to-Analog Converter (DAC)

UDA1321

responds with the appropriate settings via the audio device

class for the audio related parts or via the HID class for the

HID related inputs and outputs of the UDA1321.

A HID descriptor is necessary to inform the host about the

conception of the user interface. The host communicates

via the HID device driver using either the control pipe or

the interrupt pipe. The UDA1321 uses USB endpoint 0

(control pipe) to respond to the HID specific ‘Get/set report

request’ to receive or transmit data from or to the

UDA1321. The UDA1321 uses the status interrupt

endpoint as interrupt pipe for polling asynchronous data.

The UDA1321 is a high-speed device. The maximum

transaction size is 64 bytes per USB frame and the polling

rate is defined at a maximum of every 1 ms.

The host requests the configuration descriptor which

includes the standard interface descriptor, the HID

endpoint descriptor and the HID descriptor. The HID

device driver of the host then requests the report

descriptor.

Report descriptors are composed of pieces of information

about the device. Each piece of information is called an

item. All items have a 1-byte prefix that contains the item

tag, type and size. In the UDA1321 only the short item

basic type is used.

The hosts HID device driver will parse the report descriptor

and the defined items. By examining all of these items, the

HID class driver is able to determine the size and

composition of data reports from the device.

The main items of the UDA1321 are input and output

reports. Input reports are sent via the interrupt pipe

(UDA1321 USB address 3). Input and output reports can

be requested by the host via the control endpoint (USB

address 0).

The UDA1321 supports a maximum of three pushbuttons,

which represents a certain feature of the UDA1321. If

pressed by the user the pushbutton will go to its ‘ON’ state,

if not pressed the pushbutton will go back to its ‘OFF’ state.

The UDA1321 supports a maximum of two outputs for e.g.

user LEDs.

For more information about the input and output functions

of the UDA1321 see the application documentation of the

device.

Controlling the USB Digital-to-Analog Converter

(DAC)

This section describes the functionality of the feature unit

of the UDA1321. The mapping of this functionality onto

USB descriptors is as implemented in the firmware.

The sound features as defined in the

“USB Device Class

Definition for Audio Devices” are mapped on the UDA1321

specific feature registers by the microcontroller. These

specific sound features are:

• Volume control (separate for left and right stereo

channels, no master channel)

• Mute control (only master channel)

• Treble control (only master channel)

• Bass control (only master channel)

• Dynamic bass boost control (only master channel).

These specific features can be activated via the host

(audio device class requests) or via the GP pins (HID plus

audio device class requests). Via the I2C-bus the user is

able to download the necessary configuration data for

different applications (definition of the function of the GP

pins, with or without digital I/O functionality, etc.).

The mapping and control of the standard USB audio

features and UDA1321 specific features is described

below.

VOLUME CONTROL

Volume control is possible via the host or via predefined

GP pins. The setting of 0 dB is always referenced to the

maximum available volume setting. Table 3 gives the

mapping of wVolume value (as defined in the

“USB

Device Class Definition for Audio Devices”) upon the

actual volume setting of the USB DAC. When using the

UDA1321, the range is 0 down to

−60 dB (in steps of 1 dB)

and

−∞ dB. Independant control of ‘left’/’right’ volume is

possible. It should be noted that wVolume bits B7 to B0

are not used. Values above 0 dB are returned as 0 dB.

The volume value at start-up of the device is defined in the

selected configuration map.

Balance control is possible via the separate volume control

option of both channels. Therefore the characteristics of

the balance control are equal to the volume control

characteristics.

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