8085 Microprocessor

• It is a 8 bit microprocessor
• It was invented in 1974
• It is 40 pin IC
• 64 KB RAM
• Input voltage 5 volt DC supply

Below is pin description of  all 40 pins

1. Pin 1 & 2:  X1 & X2 is a clock frequency pin , oscillator is connected on this pin to generate clock pulse . Clock frequency upto 8 Mhz .
2. Pin 3 : Reset out , by using this pin micro controller can reset other peripheral.
3. Pin 4 & 5 : SOD & SID these pins are use as serial data communication, SOD= serial output data line , SID= serial input dataline.
4. Pin 6 to 10 : These are interrupt lines of microprocessor.  

TRAP : It is the highest priority interrupt.
RST 7.5, RST 6.5, RST 5.5 - These are high to low priority after trap interrupt respectively.
INTR : This is lowest priority pin .

   5. Pin 11: INTA this pin is interrupt acknowledgement pin .
   6. Pin 12 to 19 : AD0 to AD7 these are bidirectional pin , these are used for first 8 bit address and and 8 bit data pins.
    7. Pin 20 : This pin is use for 5 volt dc supply to microprocessor.
    8. Pin 21 to  28 : A8 to A15 these are address lines of microprocessor.
    9. Pin 29 and 33 : S0 and S1  these are use as status signal ,
                 S0      S1
                 0        0            this shows no operation
                 0        1            Read  instruction
                 1        0           Write instruction
                 1        1            Opcode fetch



10. Pin 30: ALE ( adderss latch enable ) this is use for separate address and data from AD0 to AD 7
11. Pin 31 :  WR : this is write instruction given by microprocessor to memory or input / output, this depend on IO/ M pin status.
12. Pin 32: RD : this is read instruction given by microprocessor to memory or input / output, this depend on IO/ M pin status.
13. Pin  34 : IO / M  this is pin use to indicate that which of these memory or IO device is  in use for
microprocessor.
14. Pin 35, 38, 39, : READY , HLDA , HOLD
      these are use for DMA transfer .
15 Pin 36: RESET IN this pin use to reset 8085.
16. Pin 37: CLOCK OUT  this pin use by 8085 to gives clock pulse to other devices.
17. Pin 40: VCC : this is ground pin with respect to 5 volt supply pin no.20.

Architecture of 8085

Description of 8085 -

• Interrupt control unit- This unit is use to deal with all types of interrupts and also gives interrupt service acknowledgement from its pin INTA.
• Serial I/O control unit- This unit is use to deal with all serial input and output data from microprocessor.
• Registers - There are six registers  B ,C ,D, E, H ,L all are 8 bit register, we can use them alone for holding 8 bit data whereas to handle 16 bit data we use pair of them

        BC       16bit

        DE       16bit

        HL       16bit
     
    SP(stack pointer 16 bit) - This is special purpose register , it stores the address of last program request in a stack . Stack is a reserved memory to store data.

    PC(program counter 16 bit)- This is use to store address of the  instruction to be fetched  in the program.

   Increment / Decrement  adderss latch - It is not use for programmer , it only for 8085 to store different address.

• Accumulator(8 bit ) - It is special type of register, all arithmetic operation like add, subtract, are perform in it. It also known as A register.
• Flag register(8 bit) - Flag register shows status of the 8085 program is running , it shows by 8085 , fig below shows 5 flag register use in 8085.

  

S(sign bit)- It show result is positive or negative. S=0 (positive)    S= 1 (negative)

Z(zero bit)- It show result is zero or not.

AC(auxiliary carry)-That is carry from the 3rd bit to 4th is also indicated.

P(parity bit)-It indicates whether the result contains odd number of 1s or even no. of 1s.

CY(carry flag)-It indicates whether there is carry or not after an arithmetic and logical operation,

• Timing and control unit- This unit is brain of the 8085, it gives all control related signals and all that .DMA transfer and many other work done by this unit.
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Diode & its Application

                                         Ideal diode

The key function of an ideal diode is to control the direction of current flow. Current passing through a diode can only go in the one direction, called  the forward direction. Current trying to flow the reverse direction is blocked. They're like the one way valve of electronics.

If the voltage across a diode is negative , no current can flow , and the ideal diode looks like an open circuit. In such a situation , the diode is said to be off or reverse biased.

As long as the voltage across the diode isn't negative, it'll "turn on" and conduct current . Ideally a diode would act like a short circuit ,if it was conducting current. When a diode is conducting current it's forward biased.

Circuit Symbol

Every diode has two terminals connections on each end of the components and those terminals are polarized, meaning the two terminals are distinctly different . Its important not to mix the connections on a diode up. The positive end of a diode is called the anode , and the negative end is called the cathode. Current can flow from the anode end to cathode , but not the other direction. If you forget which way current flows through a diode , try to remember the mnemonic ACID . "anode current is diode".

The circuit symbol of a standard diode is a triangle butting up against line.

Introduction Inductor

                                            Inductor

 When electrical current flows through a wire conductor, a magnetic flux is developed around the conductor producing a relationship between the direction of this magnetic flux which is circulating around the conductor and the direction of the current flowing through the same conductor . This well known relationship between current and magnetic flux direction is called "Fleming's left hand rule"

         But there is also another important property relating to a wound coil that also exists, which is that a secondary voltage is introduce into the same coil by the movement of the magnetic flux as it opposes or resists any changes in the electrical  current flowing it. 

   

         In its most basic form, an inductor is nothing more than a coil wire around a central core. For most coils the current (i) flowing through the coil produces a magnetic flux around it that is proportional to this flow of electrical current.

 

The inductor also called a choke , is another passive type electrical component which is just a coil of wire that is designed to take advantage of this relationship by inducing a magnetic field in  itself or in the core as  a  result of the current passing through the coil . This results in  a much stronger magnetic field than one that would be produced by a simple coil of wire.

Inductors are formed with wire tightly wrapped around a solid central core which can be either a straight cylindrical rod or a continuous loop or ring to concentrate their magnetic flux.

The schematic symbol for a inductor is that of a coil of wire so therefore , a coil of wire can also be called an inductor. Inductor usually are categorised according to the type of inner core they are wound around ,for example  hollow core , solid iron core or soft ferrite core with the different core types being distinguished by adding continuous or dotted parallel lines next to the wire coil as shown below.