Product specifications

Design Guide - VT82C694X Apollo Pro133 with VT82C686A
Preliminary Revision 0.5, November 19, 1999 Appendix A - SPKR Strapping Application Circuits
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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.
100 ohm
VCC3
VT82C686A
(South Bridge)
SPKR
JSPEAK
Header
1X3
V5
1K ohm
4.7K ohm
2K ohm
VCC
Q1
3904
Speaker
Speaker circuit
Jumper Strapping circuit
JSPEAK
1-2
2-3
SDD Function
Audio/Game
SDD[15..0]
1
3
2
Figure A-1. VT82C686A SPKR Pin Transistor Driver Solution (I)
VCC3
VT82C686A
(South Bridge)
SPKR
JSPEAK
Header
1X3
V5
1K
4.7K
2K
Speaker circuit
Jumper Strapping circuit
JSPEAK
1-2
2-3
SDD Function
Audio/Game
SDD[15..0]
Speaker
74HCT05
1 2
22
3
1
2
Figure A-2. VT82C686A SPKR Pin Inverter Driver Solution (II)