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SOFTWARE ARCHITECTURE OF THE8088 AND 8086 MICROPROCESSORS •
2.1 Microarchitecture of the 8088/8086Microprocessor
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2.2 Software Model of the 8088/8086Microprocessor
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2.3 Memory Address Space and DataOrganization
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2.4 Data Types
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2.5 Segment Registers and Memory Segmentation
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2.6 Dedicated, Reserved, and General-UsedMemory
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2.7 Instruction Pointer
SOFTWARE ARCHITECTURE
OF THE 8088 AND 8086
MICROPROCESSORS
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2.8 Data Registers
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2.9 Pointer and Index Register
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2.10 Status Register
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2.11 Generating a Memory Address
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2.12 The Stack
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2.13 Input/Output Address Space
2.1 Microarchitecture of the8088/8086 Microprocessor
•^
8088/8086 both employ
parallel processing
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8088/8086 contain two processing unit – the
bus
interface unit
(BIU) and
execution unit
(EU)
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The bus interface unit is the path that 8088/8086connects to external devices.
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The system bus includes an 8-bit bidirectional databus for 8088 (16 bits for the 8086), a 20-bit addressbus, and the signal needed to control transfers overthe bus.
2.1 Microarchitecture of the8088/8086 Microprocessor
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2.1 Microarchitecture of the
088/8086 Microprocessor
•^
Components in BIU– Segment register– The instruction pointer– Address generation adder– Bus control logic– Instruction queue
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Components in EU– Arithmetic logic unit, ALU– Status and control flags– General-purpose registers– Temporary-operand registers
2.1 Microarchitecture of the8088/8086 Microprocessor
2.2 Software Model of the8088/8086 Microprocessor
•^
8088 microprocessor includes 13 16-bit internalregisters.– The instruction pointer, IP
- Four data registers, AX, BX, CX, DX
- Two pointer registers, BP, SP
- Two index registers, SI, DI
- Four segment registers, CS, DS, SS, ES -^
The status register, SR, with nine of its bitsimplemented for status and control flags.
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The memory address space is 1 Mbytes and the I/Oaddress space is 64 Kbytes in length.
2.2 Software Model of the8088/8086 Microprocessor
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2.3 Memory Address Space and
Data Organization
•^
Even- or odd-addressedword– If the least significant bit of
the address is 0, the wordis said to be held at aneven-addressed boundary.
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Aligned word or misalignedword
2.4 Data Types
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Integer data type– Unsigned or signed integer– Byte-wide or word-wide integer
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The most significant bit of a signed integer is a sign bit.– A zero in this bit position identifies a positive number.
2.4 Data Types
•^
The range of a signed byte integer is +127 ~ -128.
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The range of a signed word integer is +32767 ~ -32768.
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The 8088 always expresses negative numbers in2’scomplement.
2.4 Data Types
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EXAMPLE:^ – A signed word integer equals FEFF16. What decimal
number does it represent?
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Solution:^ – FEFF
16
2
- The most significant bit is 1, the number is negative and
is in 2’s complement form.
- Converting to its binary equivalent by subtracting 1 from
the least significant bit
- Then complement all bits give:
16
= -
= -257 2
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2.4 Data Types
•^
The 8088 can also process data that is coded as binary-coded decimal (BCD) numbers.
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BCD data can be stored in packed or unpacked forms.
2.4 Data Types
•^
EXAMPLE:^ – The packed BCD data stored at byte address 01000
16
equals 10010001
. What is the two digit decimal number? 2
•^
Solution:^ – Writing the value 10010001
2
as separate BCD digits
gives
2
BCD
BCD
10
2.4 Data Types
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The ASCII(American StandardCode forInformationInterchange) digit
2.4 Data Types
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EXAMPLE:^ – Byte addresses 01100
16
through 01104
16
contain the
ASCII data 01000001, 01010011, 01000011, 01001001,and 01001001, respectively. What do the data stand for?
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Solution:^ – Using the ASCII table, the data are converted to
ASCII code:
2
= A
– (01101H) = 01010011
2
= S
– (01102H) = 01000011
2
= C
– (01103H) = 01001001
2
= I
– (01104H) = 01001001
2
= I
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