Product specifications

Design Guide - VT82C694X Apollo Pro133 with VT82C686A

Preliminary Revision 0.5, November 19, 1999 Appendix B - Audio Codec and Game/MIDI Port Layout

Guidelines

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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.

Game/MIDI

MIC_INLINE_INLINE_OUT

VIA

VT82C686A

(South Bridge)

VIA

VT1611A

(Audio Codec)

AC'97 Link

Game/MIDI

CD_IN

Header

Audio Output

Audio Input

Audio

Amplifier

Figure B-1. AC’97 Audio Codec and Game/MIDI Port Block Diagram

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.