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Appendix B - Audio Codec and Game/MIDI Port Layout Guidelines
B.1 Introduction
This document describes the Printed Circuit Board (PCB) layout recommendations for VIA VT1611A (AC'97 audio codec) and
Game/MIDI port in a motherboard design. The main focus is on how to improve the audio quality. Electromagnetic interference
(EMI) issues are not considered in the document. The layout guidelines of component placement, power and ground planes and
signal routing for VT1611A and Game/MIDI port (using a stacked LINE_OUT, LINE_IN, MIC_IN and Game/MIDI IO
connector) on a motherboard are described in detail in the following sections.
VIA VT1611A 18-bit Σ∆ audio codec conforms to the AC'97 2.1 specification with excellent analog performance. Refer to
VT1611A datasheet for more detail. Figure B-1 shows a typical single audio codec function block diagram and the direct
connections between the VT82C686A south bridge controller and the Game/MIDI port. Audio input/output signals are processed
by VT1611A audio codec. Through the AC'97 link, VT1611A audio codec is controlled by VIA VT82C686A south bridge
controller.
LINE_OUT
LINE_IN
Game/MIDI
Reference AC'97 audio codec and Game/MIDI port schematic is shown in the end page of this appendix. The reference schematic
shows an applicable AC'97 audio codec circuit. Five audio input circuits and one audio output circuit are applied. The
connections between VT82C686A and the Game/MIDI port are also shown in the schematic.
Preliminary Revision 0.5, November 19, 1999
Guidelines
Audio Output
Audio
Amplifier
Audio Input
CD_IN
Header
MIC_IN
Figure B-1. AC'97 Audio Codec and Game/MIDI Port Block Diagram
Design Guide - VT82C694X Apollo Pro133 with VT82C686A
VIA
VT1611A
(Audio Codec)
A
M
R
99
Appendix B - Audio Codec and Game/MIDI Port Layout
AC'97 Link
VIA
VT82C686A
(South Bridge)
Game/MIDI
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