PRELIMINARY DATA SHEET
2.1.6. General Purpose I/O
The GPIO pins are used to connect keys which are
related to the USB HID class or for vendor-specific
control functions and LEDs in order to indicate on/off
states for example. The standard configuration defines
the GPIOs as four input pins (GPIO0...GPIO3) and
four output pins (GPIO4...GPIO7). The function of the
input pins is shown in Table 2–2.
Table 2–2:
Standard Key Configuration
Pin
GPIO0
GPIO1
GPIO2
GPIO3
Function
Volume Up
Volume Down
MuteToggle
BassBoost Toggle
Key
Code
1
2
4
8
Usage
ID
E9
EA
E2
E5
2.1.5.5. Analog Volume Control
The analog volume control covers a range from 0 dB to
−
75 dB plus an additional mute position.
The analog step size is split into a 3-dB and a 1.5-dB
range:
−
75 dB...
−
54 dB:
−
54 dB...0 dB:
3 dB step size
1.5 dB step size
The overall volume system, however, consists not only
of the analog volume. An additional digital volume con-
trol allows a step size of 0.5 dB over the complete
range. See Section 2.2.2.7. “Volume and Balance Con-
Please note that analog input signals (AUXL, AUXR)
do not have the additional digital volume control.
2.1.5.6. Line-out/Headphone Amplifier
The line-out/headphone amplifier output is provided at
the OUTL and OUTR pins connected either to stereo
headphones or to the power amplifier within an USB
speaker. The stereo headphones require external
47-
Ω
serial resistors in both channels. See Section 4.
The keys are polled by the microcontroller and the cor-
responding key codes are transmitted to the host on
request. The relation between key code and usage ID
(see Universal Bus HID Usage Tables, Version 1.0,
Chapter 14 – Consumer Page) is defined in the HID
report descriptor (see Section 2.2.1.4. “HID Report
host along with the configuration descriptor during the
bus enumeration.
When the device is not connected to USB, the func-
tionality of the volume-control and mute pins are pre-
served. In this case, however, the parameters are
directly transferred to the DSP-core. This allows using
the device in stand-alone mode providing volume and
mute control for analog sources.
The output pins are not predefined and therefore not
related to any USB functions. They can be set or reset
by vendor-specific software.
The standard configuration can be changed also by
vendor-specific USB software, but in this case, Table
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