The document describes the pin diagram and internal architecture of the 8086 microprocessor, a 16-bit processor with a 16-bit data bus, 20-bit address bus, and registers including general purpose, pointer, base, index, and segment registers. It also provides details on the pins for address, data, control signals, interrupts and their functions. The pin diagram and architecture of the 8086 is compared to the older 8085 8-bit microprocessor.
3. 8086 is a 16-bit microprocessor with a 16-bit data bus & 20 bit
Address bus.
AD15-AD0 Multiplexed address(ALE=1)/data bus(ALE=0).
A19/S6-A16/S3 (multiplexed)
High order 4 bits of the 20-bit address OR status bits S6-S3.
M/IO Indicates if address is a Memory or IO address.
RD When 0, data bus is driven by memory or an I/O device.
WR If 0, Microprocessor is driving data bus to memory or an I/O
device.
ALE (Address latch enable)
4. DT/R (Data Transmit/Receive) Data bus is transmitting/receiving
DEN (Data bus Enable) Activates external data bus buffers.
INTR When 1 and IF=1, microprocessor prepares to service
interrupt. INTA becomes active after current instruction completes.
INTA Interrupt Acknowledge generated by the microprocessor in
response to INTR. Causes the interrupt vector to be put onto the data
bus.
NMI Non-maskable interrupt. Similar to INTR except IF flag bit is
not consulted and interrupt is vector
5. MN/ MX Select minimum (5V) or maximum mode (0V) of operation.
BHE Bus High Enable. Enables the most significant data bus bits (D 15 -D 8 )
READY Used to insert wait states into the microprocessor.
RESET Microprocessor resets if this pin is held high for 4 clock periods.
TEST An input that is tested by the WAIT instruction.
HOLD Requests a direct memory access (DMA). When 1, microprocessor stops
and
places address, data and control to the DMA.
HLDA Indicates that the microprocessor has entered the hold state.
R0/GT1 & R0/GT0 Request/grant pins request/grant direct memory accesses (DMA) during
maximum
mode operation.
LOCK Lock output is used to lock peripherals off the system.
6. 8086 REGISTERS
GENERAL PURPOSE REGISTERS
AX - 16-BIT ACCUMULATOR, CONTAINS AH AND AL
BX - BASE G.P. REGISTER, CONTAINS BH AND BL SUBREGISTERS.
CX - 16-BIT COUNTER REGISTER, CONTAINS CH AND CL
DX - DATA REGISTERR, CONTAINS DH AND DL SUBREGISTERS.
POINTER REGISTERS
IP - THE INSTRUCTION POINTER REGISTER.
SP - THE STACK POINTER REGISTER.
BASE REGISTERS
BX - BASE G.P. REGISTER (ALSO A GENERAL PURPOSE REGISTER).
BP - BASE POINTER REGISTER.
7. 8086 REGISTERS
INDEX REGISTERS
SI - SOURCE INDEX REGISTER.
DI - DESTINATION INDEX REGISTER.
SEGMENT REGISTERS
CS - CODE SEGMENT REGISTER.
SS - STACK SEGMENT REGISTER.
DS - DATA SEGMENT REGISTER - DEFAULT FOR DATA ACCESS.
ES - EXTRA SEGMENT REGISTER.
COMMON SEGMENT/OFFSET PAIRS
SS:SP - THE STACK POINTER.
CS:IP - THE PROGRAM COUNTER.
8.
9. Parameter 8085 Microprocessor 8086 Microprocessor
Definition The 8085 is an
accumulator based 8-
bit microprocessor
which can process 8-
bit of data at a time.
The 8086 is a register
based 16-bit
microprocessor which
can process 16-bit of
data at a time.
Microproce
ssor type
The 8085
microprocessor is an
8-bit accumulator
based microprocessor.
The 8086
microprocessor is a 16-
bit general purpose
register based
microprocessor.
Data bus
size
The 8085
microprocessor has a
data bus of 8-bit size.
The size of data bus of
8086 microprocessor is
16- bit.
Comparison of 8085 and 8086
10. Parameter 8085 Microprocessor 8086 Microprocessor
Address bus
size
The size of address bus of
8085 microprocessor is 16-
bit.
The size of address bus of
8086 microprocessor is 20-
bit.
ALU
(Arithmetic
Logic Unit)
size
The 8085 microprocessor
has an 8-bit ALU.
The 8086 microprocessor has
16-bit ALU.
Clock
frequency
The 8085 microprocessor
has an on-chip oscillator of
3 MHz.
The 8086 microprocessor is
available in three version
with a clock speed
(frequency) of 5 MHz, 8 MHz
and 10 MHz.
Number of
transistors
The 8085 microprocessor
consists of 6500
transistors in its structure.
The 8086 microprocessor
consists of 29000 transistors.
Comparison of 8085 and 8086
11. Operations The 8085 microprocessor can
perform addition, subtraction,
increase, decrease, compare,
AND, OR, X-OR, shift and
complement. But, it does not
support multiplication and
division.
The 8086 microprocessor is able to
perform all the operations of 8085
microprocessor and also
multiplication and division.
Number of flagsThe 8085 microprocessor has
5 flags, named carry, auxiliary
carry, parity, zero and sign flag.
The 8086 microprocessor has 9 flags,
named carry, auxiliary carry, parity,
zero, sign, trap, interrupt, direction,
and overflow flag.
Memory
segmentation
The 8085 microprocessor does
not support memory
segmentation.
The 8086 microprocessor supports
memory segmentation, i.e. the
memory of 8086 microprocessor is
segmented which means the 20-bit
address bus can access 1 MB of
memory but it uses only four 64 kB
segments from it.
12. Modes of
operation
The 8085 microprocessor
supports only a single
mode of operation.
The 8086 microprocessor
supports two modes of
operation viz. minimum mode
and maximum mode.
Pipelining
architecture
The pipelining
architecture is not
supported by the 8085
microprocessor.
The 8086 microprocessor
supports pipelining
architecture.
Instruction
queue
8085 microprocessor
does not have an
instruction queue.
8086 microprocessor has an
instruction queue of 6 bytes
which is stored in FIFO (First In
First Out) register.
Cost 8085 microprocessor is
cheaper.
8086 microprocessor is
relatively expensive than 8085
microprocessor.
