Intel 8088 microprocessor was
released in 1979, or one year after the Intel 8086 CPU. Both processors have
the same architecture, and the only difference of the 8088 CPU from the 8086 is
the external data bus width - it was reduced from 16 bits to 8 bits. The 8088
CPU uses two consecutive bus cycles to read or write 16 bit data instead of one
bus cycle for the 8086, which makes the 8088 processor to run slower. On the
plus side hardware changes to the 8088 CPU made it compatible with 8080/8085
support chips.
The 8088 microprocessor has
16-bit registers, 16-bit internal data bus and 20-bit address bus, which allows
the processor address up to 1 MB of memory. The 8088 uses the same segmented
memory addressing as the 8086: the processor can address 64 KB of memory
directly, and to address more than 64 KB of memory the CPU has to break the
update into a few parts - update up to 64 KB of memory, change segment
register, update another block of memory, update segment register again, and so
on.
- Processor Speed 8MHz
- Circuit Size 3.0 Microns
- Transistors 29000
- +5V Power Required
- 40 Pin DIP
- Data Bus Width 8 bits
- Address Bus Width 20bits
- Registers Size 16bits
- Memory Size 1 MB
Block Diagram
The 8086 microprocessor has two
sections that are E.U and BIU.
E.U Execution Unit
E.U unit performs the following
functions.
- It performs the logic and
athematic operation on memory or register.
- It receives the instruction from
pre fetch queue and decodes it.
- It stores the information
temporary in the register array.
- The execution unit consists of
register array unit ALU and CU instruction pointer unit. The register array
unit stores the data or information or instructions temporary. This unit
consists of many registers which stores the data.
The ALU and CU perform the
mathematical and logical operations on the data and also control all the
functions of the execution and bus interface unit.
Parts of E.U
- Control Circuit
- Instruction Decoder
- ALU
- General Purpose Register
- Special Purpose Register
- Control Circuit
The control circuit controls all
the operations and flow of data inside the microprocessor.
Instruction Decoder
The instruction decoder works to
translate or decode the instructions which are fetched from the memory. After
translation it places the instructions in a series to perform the required
task.
ALU
This is a 16 bit unit which
performs the AND, OR, Exclusive, Addition, Subtraction, Increment, Decrement,
Complement and Shift functions.
General Purpose Registers
The EU has 8 general purpose
registers. Which are named as AL, AH, BL, BH, CL, CH, DL, and DH these are all
8 bit registers but these can also be used as 16 bit registers, when we take
the different pairs of these registers. The possible pairs are
AL, AH = Ax
BL, BH = Bx
CL, CH = Cx
DL, DH = Dx
AL register is also called
accumulator because it has some characteristics different from other general
purpose registers.
