Microprocessor systems 8085(2)

Microprocessor SystemMicroprocessor System
ByBy
Engr.Shafiullah SoomroEngr.Shafiullah Soomro
safiullah123@gmail.comsafiullah123@gmail.com
SESSION OF Intel 8085

History of Intel MicroprocessorsHistory of Intel Microprocessors
Before 8085Before 8085
INTEL 4004
1969
16 Pins DIP Package
•Clock speed : 108 KHz
* Number of transistors:
2300
•4-bit register and 4-bit data bus.
The world first
microprocessor
INTEL 8008
1972
18 Pins DIP Package
•Clock speed : 800 KHz
* Number of transistor:
3500
* 8-bit register and 8-bit data bus.
INTEL 8080
1974
40 Pin DIP Package
•Clock speed : 2 MHz
* Number of transistor:
4500
•8-bit registers
•16-bit address bus and an 8-bit data
bus

INTEL 8085 MicroprocessorINTEL 8085 Microprocessor
• Year 1977
• Enhancement of 8080
• 40 Pins DIP Package
• The 8085 uses approximately 6,500
transistors
• Clock Speed: Max 6 MHz
• 8-bit Data Bus & 16 Bit Address Bus

8085 INTRODUCTION8085 INTRODUCTION
The features of INTEL 8085 are :
• It is an 8 bit processor.
• It is a single chip N-MOS(N Type Metal Oxide Semiconductor) device with 40 pins
DIP Package.
• It uses all instructions of 808 therefore it is program compatible with 8080
• It has multiplexed address and data bus.(AD0-AD7)
• It works on single 5 Volt dc power supply.
• The maximum clock frequency is 6 MHz while minimum frequency is 500kHz.
• It provides 74 instructions with 5 different addressing modes, Two new instruction
has been added in 8085, for taking advantage of added hardware

8085 INTRODUCTION8085 INTRODUCTION
► It provides 16 address lines so it can access 2It provides 16 address lines so it can access 2^^16 =64K16 =64K
bytes of memory.bytes of memory.
► It generates 8 bit I/O address so it can access 2It generates 8 bit I/O address so it can access 2^8=256^8=256
input ports.input ports.
► It provides 5 hardware interrupts:TRAP, RST 5.5, RST 6.5,It provides 5 hardware interrupts:TRAP, RST 5.5, RST 6.5,
RST 7.5,INTR.RST 7.5,INTR.
► It provides Acc ,one flag register ,6 general purposeIt provides Acc ,one flag register ,6 general purpose
registers and two special purpose registers(SP,PC).registers and two special purpose registers(SP,PC).
► It provides serial lines SID ,SOD.So serial peripherals canIt provides serial lines SID ,SOD.So serial peripherals can
be interfaced with 8085 directly.be interfaced with 8085 directly.

8085 Pin Diagram8085 Pin Diagram
Note: you may refer to Fig 8-2 (a) on page 209 of
Microprocessor Fundamentals by Roger

How Would you identify PinHow Would you identify Pin
Numbers of DIP IC Package?Numbers of DIP IC Package?

Short Description of Pin DiagramShort Description of Pin Diagram
Note: you may refer to Fig 8-2 (b) on page 210 of
Microprocessor Fundamentals by Roger

8085 Pin Diagram Description(1/7)8085 Pin Diagram Description(1/7)
ADDRESS BUS, DATA BUS & ALE
• More functions then 8080 are added therefore less number of pins remain,
therefore It has multiplexed address and data bus.(AD0-AD7) from Pin 12
through 19.
• Least Significant 8 Lines of Address Bus shared with 8-bit Data Bus.
• Multiplexed means selecting one at a time, First pins 12-19 work as
Address Bus to send address then works as Data Bus to carry Data.
• When these Pins worked as Data Bus and When as Address Bus is
Decided by ALE (Address Latch Enable) Output Pin Number 30 Signal.
• When ALE = 1 its Adress, when ALE = 0 its Data.

8085 Pin Diagram Description (2/7)8085 Pin Diagram Description (2/7)
Power & Clock Signals
• 8085 MPU works on Single +5V Power Supply
• Pin 40 & 20: Vcc is Power and Vss is Ground
• Pin 1 & 2 : X1 & X2 are Input pins that are connected from a crystal to the
internal clock circuitry of 8085 MP
• Pin 37: CLK is a Output Pin and it is used for timing & synchronization of
other peripherals by MP
Crystal
Frequency A
X1
X2
8085 MPU
Internal Clock
Circuitry
Frequency ½ A

RESTART SIGNALS
• Pin 36: RESET IN is Input Pin if it is 0 then it will reset MPU and set
Program counter to address 000H
•Data Bus Address Bus and Control lines are TRI-STATED during a Reset.
Tri-state means MP will release their control & they are isolated from MP,
and any other peripheral can take control of them.
•Pin 3: RESET OUT is a Output pin, if it is 1 then it will inform all peripherals
that System is restart
•

SERIAL INPUT & OUTPUT
SIGNALS
• 8085 has two pins for serial data
input and output so, serial devices
can be directly interfaced with 8085
• Pin 5: SID is a Serial Input Pin, it
is used to input serial data (i.e. one
bit at a time) to MSB of
Accumulator. This Pin is control by
RIM instruction
• Pin 4: SOD is Serial Output Pin, it
is used to send serial data, by SIM
instruction
Figure: 8-7 From Book Page 217

READY & HOLD SIGNALS
• Pin 35: is READY input port, it is used by other peripherals to inform MP
that they are ready to send or receive data
• If READY pin is low means 0 then MP will be in wait state until again the
REDY signal is high 1, this mostly occur frequently because of low speed of
other peripherals
• Pin39: is HOLD input signal, used by other peripherals to request MP that
they want to use the Data & Address Bus (may occur in DMA operations)
• Upon receiving HOLD signal, MP will first finish its own data transfer on
busses then
• Address Bus, Data Bus, RD, WR, IO/M pins are Tri-stated (means isolated
from MP)
• Pin 38: HOLDA, is a Output signal, it is an Acknowledgement to peripheral
requesting HOLD, and it inform the requesting peripheral that MP is going to
release the control of Buses in next clock cycle

MACHINE CYCLE
• Pins 33: S1, 29: S0, 34:
IO/M are Output signals that
are used to inform other
peripherals that what type of
machine cycle MP is running
Figure 8-3 Page 211

Interrupts SIGNALS
An interrupt is a signal that alter the
normal execution of Microprocessor
In 8085 there are 5 interrupts Inputs
TRAP, RST 7.5, RST 6.5, RST 5.5, INTR,
through these interrupt signals can be
sent to MP
When MP receive interrupt it
Acknowledged the interrupting device
through INTRA output signal
Those interrupts that can be enabled or
disabled by software are called Maskable
interrupts e.g.: RST 7.5, RST 6.5, RST
5.5, INTR
Those interrupts that can not be disabled
are called Non-Maskable interrupts e.g.
TRAP
Fig 8-6 page 216

End of PIN Diagram DescriptionEnd of PIN Diagram Description

8085 ARCHITECTURE8085 ARCHITECTURE

Functional Blocks of 8085Functional Blocks of 8085
ARCHITECTUREARCHITECTURE
The various functional blocks of 8085 are as follows:
1. Registers
2. Arithmetic logic unit
3. Data/Address buffer
4. Incrementer/decrementer address latch
5. Interrupt control
6. Serial I/O control
7. Timing and control circuitry
8. Instructions decoder and machine cycle encoder.

Description of 8085 ARCHITECTURE (1/8)Description of 8085 ARCHITECTURE (1/8)
1. ACCUMULATOR
This 8-bit register is the most important one amongst all the registers of 8085. Any
data input/output to/from the microprocessor takes place via the accumulator
(register). It is generally used for temporary storage of data and for the placement
of final result of arithmetic/logical operations. Accumulator (ACC or A) register is
extensively used for arithmetic, logical, store and rotate operations
2. TEMPORARY REGISTERS
The temporary data register of 8085 is an 8-bit register, which is not available to the
programmer, but is used internally for execution of most of the arithmetic and
logical operations.
REGISTERS OF 8085:

3. GENERAL PURPOSE REGISTERS
• The general purpose registers of 8085 are: B, C, D, E, H and L.
They are all 8-bit registers but can also be used as 16-bit register
pairs—BC, DE and HL. These registers are also known as scratch
pad registers.
• HL register pair can be used as a data pointer or memory pointer.
• General purpose registers store temporary data during program
execution, which can also be stored in different accessible memory
locations. But storing temporary data in memory requires bus access
—hence more time is needed to store. Thus it is always advisable to
store data in general purpose registers.

4. PROGRAM COUNTER
Program counter (PC) is a sixteen bit register which
contains the address of the instruction to be executed
just next. PC acts as a address pointer (also known as
memory pointer) to the next instruction. As the
processor executes instructions one after another, the
PC is incremented—the number by which the PC
increments depends on the nature of R/W memory the
instruction. For example, for a 1-byte instruction, PC is
incremented by one, while for a 3-byte instruction, the
processor increments PC by three address locations.
5. STACK POINTER
Stack pointer (SP) is a sixteen bit register which points to the ‘stack’. The stack is an
area in the R/W memory where temporary data or return addresses (in cases of
subroutine CALL) are stored. Stack is a auto-decrement facility provided in the system.
The stack top is initialized by the SP by using the instruction LXI SP, memory address.
In the memory map, the program should be written at one end and stack should be
initialized at the other end of the map—this is done to avoid crashing of program.

6. INSTRUCTION REGISTER
Program written by the programmer resides in the R/W memory. When an
instruction is being executed by the system, the opcode of the instruction is
fetched from the memory and stored in the 8-bit instruction register. The
opcode is loaded into the instruction register during opcode fetch cycle. It is
then sent to the instruction decoder.
7. INCREMENT/DECREMENT ADDRESS LATCH
This 16-bit register increments/decrements the contents of PC or SP when
instructions related to them are executed.

8. STATUS FLAGS REGISTER
It is an 8-bit register in which five bit positions contain the status of five condition flags
which are Zero (Z), Sign (S), Carry (CY), Parity (P) and Auxiliary carry (AC). Each of
these five flags is a 1 bit F/F. The flag register can’t be written into. The flag register
format is shown in Fig
Sign (S) flag: – If the MSB of the result of an operation is 1, this flag is set, otherwise it is reset.
Zero (Z) flag:– If the result of an instruction is zero, this flag is set, otherwise reset.
Auxiliary Carry (AC ) flag:– If there is a carry out of bit 3 and into bit 4 resulting from the execution of
an arithmetic operation, it is set otherwise reset. This flag is used for BCD operation and is not
available to the programmer to change the sequence of an instruction.
Carry (CY) flag:– If an instruction results in a carry (for addition operation) or borrow (for subtraction
or comparison) out of bit D7, then this flag is set, otherwise reset.
Parity (P) flag:– This flag is set when the result of an operation contains an even number of 1’s and is
reset otherwise.

ALU
• ALU is responsible for all arithmetic and logic operations
of MP.
• The ALU functions as a part which includes arithmetic
logic group of circuits. This includes accumulator, flags
F/Fs and temporary register blocks.
• 8085 does not have the above two instructions. It can
neither multiply nor divide two 8-bit numbers. The same
are executed by the processor following the process of
repetitive addition or subtraction respectively.

SERIAL I/O CONTROL
It is used to accept the serial 1 bit data by using SID and SOD signals
and it can be performed by using SIM & RIM instructions
INTERRUPT CONTROL
It accepts different interrupts like TRAP INT5.5,6.5,7.5and INTR.
ADDRESS / DATA BUFFERS
8-bit Temperory Storage for Data/Address before transmitting to or
after receiving from Data/Address Bus
INSTRUCTION DECODER & MACHINE CYLE ENCODING
This section is responsible for decoding the opcode and provide this
information to timing & control section

TIMMING AND CONTROL SECTION
The T&C section is a part of CPU and generates
timing and control signals for execution of
instructions. This section includes Clock signals,
Control signals, Status signals, DMA signals as
also the Reset section. This section controls
fetching and decoding operations. It also
generates appropriate control signals for
instruction execution as also the signals
required to interface external devices.

End of Internal Architecture ofEnd of Internal Architecture of
80858085

What are the different instruction word sizes inWhat are the different instruction word sizes in
8085?8085?
The instruction word sizes are of the following types:
 1-byte instruction
The examples are given below:
 1-byte instruction : ADD B
 2-byte instruction : MVIC, 07
 3-byte instruction : LDA 4400

Explanation of word size of instructionsExplanation of word size of instructions

ADDRESSING MODES OF 8085ADDRESSING MODES OF 8085
 Each instruction indicates an operation to be performed on certain data.
There are various methods to specify the data for the instructions, known
as ‘addressing modes’.
 Or An Addressing mode is the technique used to fetch the desired
operand during execution of an instruction
 For 8085 microprocessor, there are five addressing modes.
These are:
 Direct addressing
 Register addressing
 Register indirect addressing
 Immediate addressing
 Implicit addressing.

(a)Direct Addressing:
In this mode, the operand is specified within the instruction itself.
Examples of this type are:
LDA 4000H, STA 5513H, etc.
IN/OUT instructions (like IN PORT C, OUT PORT B, etc.) also falls
under this
category.
(b) Register Addressing:
In this mode of addressing, the operand are in the general purpose
registers.
Examples are: MOV A, B ; ADD D, etc.

(c) Register Indirect Addressing:
MOV A, M; ADD M are examples of this mode of addressing. These
instructions utilise 1-byte. In this mode, instead of specifying a
register, a register pair is specified to accommodate the 16-bit
address of the operand.
(d) Immediate Addressing:
MVI A, 07; ADI 0F are examples of Immediate Addressing mode.
The operand is specified in the instruction in this mode. Here, the
operand address is not specified.
(e) Implicit Addressing:
In this mode of addressing, the operand is fully absent. Examples
are RAR, RAL, CMA, etc.

Microprocessor systems 8085(2)

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