Intel 8088 Microprocessor

       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.