Pin configuration of 8085 microprocessor

8085 MICROPROCESSOR 

PIN CONFIGURATION 

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1)  A₈-A₁₅  :-

            These are address bus and it used for most significant bits of the memory address or 8 bits of input or output address.

2) AD₀-AD₇  :-
            These are multiplexed data/address bus. They are used for dual purpose. They transfer least significant 8 bits (LSB) of the address. Again they are used for data.

3) ALE: -
            It is address latch enable signal. It is 1 when address is passed on address bus.

4) IO/ M: -
            It is a status signal. When the address and address bus is for I/O device. It is one (high).It is zero (low).When the address on address bus is for memory.

 

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

 

 

 

 

 

  

 

 5)  RD: -

            It is zero (low) when the read operation is performing by the microprocessor.

6)  WR: -
            It is low when the data is return to the memory or input/output.

7)  READY: -
            It is used by the microprocessor to since whether a peripheral (I/O, Memory) is peripheral connected to the microprocessor ready light. If the ready signal is one (high) the peripheral is ready if is low the microprocessor weights till it become high.

8)  HOLD: -
            It indicates that another device is requesting for the use of address and data bus when hold request receive the microprocessor release the command on busses.

10)  HLDA:-

                        It is hold acknowledgement signal it indicates that the hold request has been received and the microprocessor takes over the control on busses.

11)  INTR:-

               It is an interrupt request signal among interrupt it has lowest priority when it

 Is high (1) the microprocessor suspends. It’s normal sequence of instruction after

Completing the instruction at hand it attends the interrupting device. An interrupt

Is used by input/output devices to transfer data to the microprocessor without

 Wasting it’s time.

12)  INTA:-

It is an interrupt acknowledgement signal sent by the microprocessor after INTR received.

13)  RST 5.5, RST 6.5, RST 7.5 and TRAP:-

                    These are interrupting when an interrupt is recognized. The next instruction is executed from a fixed location in the numeric. They are given below.

 

Interrupt	Memory location
TRAP	0024
RST 5.5	002C
RST 6.5	0034
RST  7.5	003C

 

            The TRAP is the highest priority interrupt. It is nonmascable interrupt. The list of interrupt according to priority is a below,

                                            TRAP

                                             RST 7.5

                                             RST 6.5

                                             RST 5.5

                                             INTR

                              

14) RESET IN :-

                             It resets the program counter to zero. The CPU is held in reset condition as long as reset is applied.

15) RESET OUT  :-

       It indicate that the CPU in being reset.

16) X1 , X2 :-                                                                                                                                                                      

                     These are the –terminals connected to the clock circuit.

17) CLK :-

                     It is clock which is indicate that the processor is in process.

18) SID  :-

                          It is a dateline for serial input.

19) SOD  :-

                     It is a dateline for serial output.

20) VCC  :-

                     +5 volts power supply.

21) VSS  :-  Ground .