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The valid register pairs are AH and AL, BH and BL, CH and CL, and DH and DL.

The 8086 Microprocessor architecture is an enhanced design of the 8085 microprocessor.

It is a 16-bit Microprocessor having 20 address lines and 16 data lines that provides up to 1MB storage.

It consists of a powerful instruction set, which provides operations like multiplication and division easily.

It supports two modes of operation, i.e.

Maximum mode and Minimum mode.

The maximum mode is suitable for a system having multiple processors and the Minimum mode is suitable for a system having a single processor.

It was the first 16-bit processor having 16-bit ALU, 16-bit registers, internal data bus, and 16-bit external data bus resulting in faster processing.

It is available in 3 versions based on the frequency of operation.

Fetch stage can prefetch up to 6 bytes of instructions and stores them in the queue.

This 8086 Microprocessor architecture has so many advanced features over the 8085 Microprocessor architecture level design which makes the unique chip design.

If you will think about the most important architecture level change, the name pipe-lining method will come to picture.

Its function is to control operations on data using the instruction decoder ALU.

EU has no direct connection with system buses as shown in the above figure, it performs operations over data through BIU.

Auxiliary flag: When an operation is performed at ALU, it results in a carryborrow from lower nibble (i.e.

D0 D3) to upper nibble (i.e.

D4 D7), then this flag is set, i.e.

D3 bit to D4 is AF flag.

The processor uses this flag to perform binary to BCD conversion.

Parity flag: This flag is used to indicate the parity of the result, i.e.

Parity Flag is set.

Zero flags: This flag is set to 1 when the result of the arithmetic or logical operation is zero else it is set to 0.

Sign flag: This flag holds the sign of the result, i.e.

Overflow flag: This flag represents the result when the system capacity is exceeded.

If it is set, then the program can be run in a single-step mode.

Interrupt flag: It is an interrupt enabledisable flag, i.e.

It is set to 1 for interrupt enabled condition and set to 0 for interrupt disabled condition.

As the name suggests when it is set then string bytes are accessed from the higher memory address to the lower memory address and vice-a-versa.

These registers can be used individually to store 8-bit data and can be used in pairs to store 16bit data.

How To Program A 8086 Microprocessor