Appendix A - Spkr Strapping Application Circuits; Figure A-1. Vt82C686A Spkr Pin Transistor Driver Solution (I); Figure A-2. Vt82C686A Spkr Pin Inverter Driver Solution (Ii) - VIA Technologies Apollo Pro133A Design Manual

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Appendix A - SPKR Strapping Application Circuits

Power-up strapping for the VT82C686A SPKR pin (pin V5) determines the function of the Secondary IDE disk data bus pins
(SDD[15..0]) to be either SDD[15..0] (SPKR strapped low) or Audio/Game port functions (SPKR strapped high). The speaker
drive circuit commonly used in PC motherboards uses a fairly small base resister (on the order of 22 ohms) into the base of a
transistor driver. This circuit, however, results in too low a voltage on the SPKR pin for the strap pullup resistor to overcome. In
this case, power up reset will always detect a low signal. Therefore, either of the two application circuits shown below in figures
A-1 or A-2 should be used to insure that both high and low strap levels are detected properly.
JSPEAK
1-2
2-3
VT82C686A
(South Bridge)
Preliminary Revision 0.5, November 19, 1999
SDD Function
Audio/Game
SDD[15..0]
V5
SPKR

Figure A-1. VT82C686A SPKR Pin Transistor Driver Solution (I)

VT82C686A
(South Bridge)
V5
SPKR
JSPEAK SDD Function
1-2 Audio/Game
2-3 SDD[15..0]

Figure A-2. VT82C686A SPKR Pin Inverter Driver Solution (II)

Design Guide - VT82C694X Apollo Pro133 with VT82C686A
Jumper Strapping circuit
JSPEAK
1K ohm
1
2
4.7K ohm
3
Header
1X3
2K ohm
Speaker circuit
Jumper Strapping circuit
JSPEAK
1
2
4.7K
3
Header
1X3
2K
1
74HCT05
Speaker circuit
97
VCC3 VCC
100 ohm
Q1
3904
VCC3
1K
Speaker
22
2
Appendix A - SPKR Strapping Application Circuits
Speaker