Transcript Slide 1

STES
Sinhgad Institute of Tech. & Science
Dept. of Computer Engg.
Pune-41
Pentium Real Mode
Prof. Mahendra Balkrishna Salunke
Asst. Prof. Dept. of Computer Engg.,
STES SITS, Narhe, Pune-41
Avenue
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What is real mode?
Address translation in Real Mode.
Registers used in Real Mode.
Instructions used in Real Mode.
Interrupt and Exception Handling
Computer Engg. Dept. STES SITS Pune
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What is Real Mode?
• The real-address mode of the Pentium
processor runs programs written for the
8086, 8088, 80186, or 80188 processors,
or for the real-address mode of Intel 286,
Intel386, or Intel486 processors.
Computer Engg. Dept. STES SITS Pune
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Address translation in Real Mode.
• Same as 8086.
• Linear Address range: 0 to 10FFEFh (1MB +
Approx 64kb)
• A20M# pin is used to mask bit A20
• As paging is not allowed this linear address
will be used as physical address
• Effective address can be of 32bit but should
not exceed 65,535
Computer Engg. Dept. STES SITS Pune
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Registers used in Real Mode
• All registers defined for 8086 plus FS, GS,
debug registers, control registers, test
registers, and floating-point unit registers.
• Pentium processor offers an operand-size
override prefix which enables access to 32bit operands.
Computer Engg. Dept. STES SITS Pune
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Instructions used in Real Mode.
• Programs executing in real-address mode
are able to take advantage of the new
application oriented instructions added to
the architecture with the introduction of the
80186, 80188, Intel 286, Intel386,
Intel486, and Pentium processors.
Computer Engg. Dept. STES SITS Pune
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Interrupt and Exception Handling
• Interrupts and exceptions in real-address mode
work much as they do on an 8086 processor.
• Interrupts and exceptions call interrupt procedures
through an interrupt vector table.
• The location and size of the interrupt table depend
on the contents of the IDTR register
• After reset, the IDTR register contains a base
address of 0 and a limit of 3FFH,
• The LIDT instruction can be used in real-address
mode to change the base and limit values in the
IDTR register.
Computer Engg. Dept. STES SITS Pune
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E-mail: [email protected]
URL: www.microsig.webs.com
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