Diagram of 8085 Microprocessor Full Details

Block and Pin Diagram of 8085 Microprocessor

Today we will read, block diagram and pin diagram of 8085 microprocessor. But before that we should know what is 8085 Microprocessor (What is 8085 Microprocessor). Come let’s know.

The 8085 microprocessor is an improved version of the 8080 microprocessor. As many pins are in the 8080 microprocessor, the same number of pins are also in the 8085 microprocessor. If there is a difference then it is that RIM and SIM are two instructions in 8085 microprocessor but not in 8080 microprocessor.

The 8085 microprocessor is a 40 pin IC (Integrated chip). It works on a frequency of 3 MHz and a supply of +5V. The microprocessor 8085 was created in 1977, using NMOS technology. Before reading Pin Diagram, we read the block diagram of 8085 microprocessor.

Topics

Block Diagram of 8085 Microprocessor (8085 Microprocessor Architecture)
(1). Register in 8085 Microprocessor
(2). Arithmetic Logical Unit (ALU)
Instruction Register/Decoder
(3). Timing and Control Unit
Description of Microprocessor 8085 Pin (Pin Diagram of 8085 Microprocessor)

Block Diagram of 8085 Microprocessor (8085 Microprocessor Architecture)

see the picture below,

(1). Register in 8085 Microprocessor

There are many types of registers in 8085 microprocessor. But before that let us understand what is register? Like, we write notes in the diary, in the same way the register in the microprocessor is also used to store the information (memory address or data).

A, B, C, D, E, H and L are general-purpose 8-bit registers. These registers are used by the programmer/user. These registers are also used to store 16-bit information. You must be thinking how? Come let’s know

How many bits are Register B and Register C? Both registers are of 8-8 bit. If, both register B and register C are used together, it will act as a 16-bit register. Because, if we use them together then they are called register-pair. B-C, D-E and H-L are register-pair.

Note that you cannot create any register-pair of your own free will except B-C, D-E and H-L.

W and Z are two 8-bit internal registers that are used only by the microprocessor. These are also called Temporary registers.

Accumulator is an 8-bit register and it is denoted by ‘A’.

Program Counter (PC): The program counter holds the memory address of the next instruction. Because, the program counter holds the address of the memory, so it is clear that if the memory address is of 16-bit then the program counter will also be of 16-bit.

Stack Pointer (SP): It follows the concept of Last In First Out (LIFO). That is, the data that will go in the end, it will be executed first. Think of it like this, when we keep the plates one on top of the other, then when we lift the plate, we will first lift the plate which was placed at the end.

What is Extrinsic Semiconductor?

It is a 16-bit register that stores the memory address. It performs two operations,

(1) PUSH Operation: When we have to put data in the stack, PUSH is used.

(2) POP Operation: POP is used when data is to be removed from the stack.

(2). Arithmetic Logical Unit (ALU)

This unit performs arithmetic (addition, subtraction, increment and decrement) and logical operations (like AND, OR, Complement etc.).

The output of arithmetic and logical operations is stored in the accumulator (register ‘A’).

Instruction Register/Decoder
When the microprocessor fetches any instruction from memory, the fetched instruction remains in the instruction register.

The instruction decoder decodes the instruction stored in the instruction register and sends it to the timing and control unit for further processing.

Flag Register: In 8085 microprocessor, flag register is used to know the status of any result or output.

Here status means whether the result/output is positive or negative, whether the carry generated in the output after the operation is performed or not etc.

There are five types of Status Flags in the Flag Register-

(1) Carry Flag (CY) (2) Parity Flag (P) (3) Auxiliary Carry Flag (AC) (4) Zero Flag (Z) (5) Sign Flag (S)

(3). Timing and Control Unit

Read the name of this unit carefully – It is understood from the words Timing and Control Unit that it works to synchronize all peripheral, internal and external devices. It means to say that they should work together when needed.

The way our brain sends signals to the parts of our body, similarly, in the microprocessor, this unit also gets the work done by sending signals to other parts.

Ready, ALE, S0, S1, HOLD, HLDA, RESETIN, RESETOUT, IO/M’ etc. We will read about these pins in Pin Description of 8085 microprocessor.

Interrupt

What is Interrupt and what are its types. These are of many types- Software interrupt, Hardware interrupt, maskable interrupt, non-maskable interrupt, vectored interrupt and non-vectored interrupt.

Serial I/O control

It is used when the microprocessor has to do serial data communication with peripheral devices. Communication is done through SID and SOD PIN.

Increment and decrement register

It is used to increase or decrease the data of the register and the position of the memory. It increases or decreases the position of data or memory by one.

Pin Diagram of 8085 Microprocessor

Pin diagram is often asked in the exam. We forget some PIN or the other. Today we will understand the pin diagram in such a way that we will not need to memorize it. Let us start,

We all know that microprocessor 8085 is a 40-pin IC. Out of 40 pins, 16-pins are for address and data bus.

In microprocessor 8085, the address-bus is of 16-bit and the data-bus is of 8-bit. If you look at the picture, you will see that the pins from AD0 to AD7 are multiplex (mixed in colloquial language). That is, AD0 to AD7 can be used as both a data bus and an address bus.

A0 to A7 pins carry lower address and A8 to A15 pins carry higher-order address.

Have you ever thought, when AD0 to AD7 pins will act as address-bus and when data-bus. After all, how does the microprocessor know whether to use the AD0 to AD 7 pins as an address bus or as a data-bus. It helps us to know the ALE (Address Latch Enable) Pin.

Address Latch Enable (ALE) Pin

ALE is a High-Enable Pin. This means that if ‘1’ is sent to this pin, then the microprocessor will understand that it has to use the AD0 to AD7 pin as an address-bus.

IO/M’ (Input/Output or Memory bar)

If IO/M’ = 1 then the microprocessor will enable the input/output device. As soon as the devices are activated, data can either be sent to the microprocessor or taken from it.

If IO/M’ = 0 then the microprocessor will communicate with the memory i.e. either store the data in memory or take data from memory.

RD’ (Read Signal)

Whenever data has to be read from memory or input/output device, then ‘0’ is sent on this signal. This is a low enable pin.

Things to remember: Signals that have a bar (‾ or ‘ ) above them are low enable signals. When you send ‘0’, it tells the microprocessor which pin has been activated.

WR’ (Write Signal)

This is also a low-enable pin. That is, when you have to do write operation on memory or input / output device, then this pin is activated by sending ‘0’ signal. The microprocessor performs the write operation.

HOLD Pin

The DMA controller sends a ‘1’ to the microprocessor instructing it to stop its current process. Free the Data-bus and Address-bus so that it can access data from memory.

HLDA’ (Hold Acknowledgment)

Because this is a low-enable pin, the microprocessor sends ‘0’ to inform the DMA controller that the request sent by the HOLD pin has been accepted.

RESETIN’

By pressing this pin, the data stored in the microprocessor gets reset. The ResetIN pin is a low-enable pin.

RESETOUT

When ‘1’ signal is given on this pin, all the external devices connected to the microprocessor are also reset.

The microprocessor will reset other devices only when the microprocessor has been reset by pressing the reset pin.

Ready

This pin is used to synchronize slow-peripherals connected to the microprocessor.

S0, S1

These are status signals, with the help of which the microprocessor 8085 is performing which operation it gets information. Look at the table given below,

S0 = S1 = Operation
0 = 0 = HALT
0 = 1 = Read
1 = 0 = Write
1 = 1 = Opcode Fetch

Whenever serial data communication has to be done, then these pins are used.

SID (Serial Input Data) Pin: Whenever the RIM instruction is executed, then the data is loaded from this pin on the 7 bit of the accumulator.

SOD (Serial Output Data) Pin: Whenever the SIM instruction is executed, the data stored on the 7th bit of the accumulator is sent to the output devices with the help of SOD pin.

CLKOUT Pin

This pin is used to synchronize peripheral devices connected to the microprocessor 8085.

TRAP, RST 7.5, RST 6.5 and RST 5.5, INTR (Interrupt Request)

Among these five, TRAP is a non-maskable interrupt. RST 7.5, RST 6.5, RST 5.5 and INTR are maskable interrupts. We will read about these interrupts in the next article.

INTA’ (Interrupt Acknowledgment)

This pin is used by the microprocessor. When the microprocessor gets an interrupt request from the INTR pin and it accepts this request. Then it gives an acknowledgment that the interrupt request has been accepted by sending a ‘0’.

Vcc

Microprocessor requires +5V power supply to operate.

X1, X2

The crystal oscillator is connected to these pins. Which constantly generates a frequency of 3 MHz for the microprocessor 8085.

Hope you have understood well the block diagram and pin diagram of 8085 microprocessor. If you have any question then please write in comment box. If you liked the article then share it with your friends.

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