DSP 104-plus, Reference Manual

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3.11 VIDEO PLAYBACK
The Geode GX1 architecture provides hardware support for the playback of video
recordings. This substantially improves the picture quality and playback frames per
second when decoding MPEG and other video files.
Video playback logic present within the Geode GX1 chip set includes colour-space
conversion logic, scaling hardware, X/Y video filters, overlay colour-key and gamma
correction.
Drivers that make use of this hardware are loaded when the Windows 95/98 graphics
drivers are installed.
3.12 AUDIO RECORDING AND PLAYBACK
The Geode GX1 architecture provides a SoundBlaster-compatible sound system.
This includes logic to record and playback .WAV files and .MID files. Drivers for the
audio functions are loaded when the Windows 95/98 display drivers are loaded.
Separate drivers are provided for Windows NT.
Due to a lack of connectors the analog to digital convertor chip shares pins on
connector J6 with the SoundBlaster audio circuitry. Appendix B describes how pins on
this connector can be assigned to one function or the other.
The TP400’s external connections are for Line In and Line Out (stereo) and
Microphone In (mono). The PC speaker (PC Beep) is also routed through the sound
system circuitry, and can be mixed with other audio streams and sent out the Line
Out outputs.
The TP400 provides power for the microphone. A voltage of about 2.2V is applied to
the microphone through a 2k2 resistor.
3.13 SPEAKER
A PC compatible loudspeaker port is implemented within the Geode GX1. This allows
for production of tones, tunes, keyboard clicks etc. PC software that uses the
speaker to generate sound will therefore operate as expected with the TP400. The
TCDEVPLUS has a small loudspeaker mounted to it and connection is made to the
TP400 via the J4 I/O cable assembly. External speakers should be connected
between the J4 signal called SPKR and VCC (+5V).
The speaker circuit is very simple: the logic level from the core logic drives the gate of
an open drain MOSFET which has its source pin connected to GND. The speaker
connects between the source and VCC, through a current limiting resistor.
The speaker signal is also sent to the audio codec, so that the PC’s beeps will be fed
to external speakers, through the LINE OUT signals (see section 3.12 for further
details).