Product specifications

Design Guide - VT82C694X Apollo Pro133 with VT82C686A
Preliminary Revision 0.5, November 19, 1999 66 Motherboard Design Guidelines
Technologies, Inc.
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2.5.6 IDE
Both Primary and secondary IDE channels have their own control signals. The Primary IDE channel has a dedicated data bus.
However, the secondary IDE data bus is multiplexed with an Audio/Game port or it can share ISA address bus SA[15:0] as
SDD[15:0]. The two options are listed below for selecting the secondary IDE data bus.
• Option 1: The secondary IDE data bus uses its own bus SDD[15:0] sharing with an Audio/Game port when the SPKR pin
is strapped low. No Audio/Game port is supported in this case since these functions are shared with the SDD[15..0] pins.
• Option 2: The secondary IDE data bus shares ISA address bus SA[15:0] as SDD[15:0] through two 74F245 transceivers
when the SPKR pin is strapped high. The sharing circuitry is shown in Figure 2-58. Audio/Game port functions are
enabled on the SDD[15:0] pins.
U1
A1
A8
A7
A6
A5
A4
A3
A2
B1
B8
B7
B6
B5
B4
B3
B2
OE#
DIR
11
12
13
14
15
16
17
18
1
19
9
8
7
6
5
4
3
2
SDD0 SA0
A1
A8
A7
A6
A5
A4
A3
A2
B1
B8
B7
B6
B5
B4
B3
B2
OE#
DIR
11
12
13
14
15
16
17
18
1
19
9
8
7
6
5
4
3
2
SDD8 SA8
74F245
74F245
U2
SDD[15..0] SA[15..0]
SA7
SA6
SA5
SA4
SA3
SA2
SA1
SA15
SA14
SA13
SA12
SA11
SA10
SA9
SDD7
SDD6
SDD5
SDD4
SDD3
SDD2
SDD1
SDD9
SDD10
SDD11
SDD12
SDD13
SDD14
SDD15
-SOE
-MASTER
Note: These 74F245 Transceivers are optional if ISA bus load is not a concern.
(From VT82C686A)
(To ISA slots)
(From VT82C686A
& to Secondary IDE)
(From VT82C686A)
Figure 2-58. ISA Bus SA[15:0] / SDD[15:0] Sharing Circuitry