112 lines
5.0 KiB
Plaintext
112 lines
5.0 KiB
Plaintext
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AST RESEARCH, INC. TECHNICAL BULLETIN #0634 08-23-90
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=============================================================================
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AST SHADOW BIOS MEMORY ADDRESSES
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The following information provides two methods of determining which memory
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range is used to shadow the system and video BIOS on AST computers equipped
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with the Shadow feature. In addition to copying the system BIOS, AST Shadow
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BIOS also has the option of copying the video BIOS. However, the video
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adapter must be an AST VGA adapter or on-board VGA. The memory range used to
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shadow the BIOS is based on the CPU type and system architecture. The memory
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locations on earlier Premium systems differ from those currently
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manufactured.
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To determine which memory locations are used by Shadow BIOS, it is necessary
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to identify the system's CPU type either by the part number of the processor
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board or using the DOS DEBUG program.
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Listed below are the steps to identify the CPU using DEBUG and which memory
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locations that system uses for Shadow BIOS. Also included are processor
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board part numbers as an alternative to running the DEBUG program.
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DEBUG
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At the DOS prompt, type: DEBUG and press the <enter> key. <Enter> is a
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prompt to press the "enter" key. At the DEBUG prompt "-", type lines 1 and
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2.
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Line 1. -OE0 7 <Enter>
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Line 2. -IE1 <Enter>
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Line 3. -nn
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Note: The number displayed on the third line identifies the CPU type.
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If this value is a number between 12 and 18, Shadow BIOS uses the
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memory locations shown in Method #2. Any other value identifies
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the use of memory locations shown in Method #1. Enter Line 4 to
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leave DEBUG.
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Line 4. -q <Enter>
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METHOD #1
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When this method is used, the system BIOS uses a 64KB block at F0000-FFFFF.
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However, when the system BIOS is shadowed, the E0000-EFFFF range is also
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reserved whether the video BIOS is shadowed or not. If the video BIOS is
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shadowed it resides in a 32KB block at E0000-E7FFF and the remaining 32KB of
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that block is reserved.
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Block Reserved Area
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Size Decimal Hex Address Between 640 - 1MB
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+------------------ +------------+ -----------------+
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| 64 KB 960 KB |+++F0000++++| SYSTEM BIOS |
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|------------------ |------------| |
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| 64 KB 896 KB |+++E0000++++| VIDEO BIOS |
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|------------------ |------------| |
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| 64 KB 832 KB | D0000 | |
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|------------------ |------------| |
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| 64 KB 768 KB | C0000 | |
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|------------------ |------------| |
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| 64 KB 704 KB | B0000 | |
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+------------------ |------------| |
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640 KB | A0000 | |
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|------------| -----------------+
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| 09FFF |
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|Base Memory |
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| 00000 |
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+------------+
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The following AST computers use this method for Shadow BIOS:
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- All Premium 386 and Premium 386C Systems.
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- Premium 386SX/16 Systems with a 202337-001 Processor Board.
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- Premium 386/25 Systems with a 202274-001 Processor Board.
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- Premium 386/33 Systems with a 202347-002 Processor Board.
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METHOD #2
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The following method is used on all remaining AST computers. When this
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method is used, the system BIOS uses a 64KB block at F0000-FFFFF, the video
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BIOS is shadowed in a 32KB block at C0000-C7FFF.
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Block Reserved Area
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Size Decimal Hex Address Between 640 - 1MB
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+------------------ +------------+ -----------------+
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| 64 KB 960 KB |+++F0000++++| SYSTEM BIOS |
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|------------------ |------------| |
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| 64 KB 896 KB | E0000 | |
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|------------------ |------------| |
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| 64 KB 832 KB | D0000 | |
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|------------------ |------------| |
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| 32 KB 800 KB | C8000 | |
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| |<7C><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>| |
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| 32 KB 768 KB |+++C0000++++| VIDEO BIOS |
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|------------------ |------------| |
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| 64 KB 704 KB | B0000 | |
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+------------------ |------------| |
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640 KB | A0000 | |
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|------------| -----------------+
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| 09FFF |
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|Base Memory |
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| 00000 |
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+------------+
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