8085 microprocessor pin configuration

       -: 8085 Microprocessor :- 

8085 microprocessor is a 8 bit microprocessor designed by Intel in 1976 using NMOS technology. It can be classified into following groups-
1-Address bus
2-Data bus
3-Control and status signal
4-Power supply and clock frequency
5-Interrupt and externally initiate signal
6-serial I/O ports

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1-Address bus :- 

                                   A8- A15 are the address buses.These are uni-directional buses.It used for the most significant bytes called high order address .It carries the most significant 8 bit of memory/IO addresses.

2-Multiplexed address/ data bus:-                                                                                 AD7 -AD0 are the multiplexed buses. These are bi directional. They serve a dual purpose they are used as a low order address bus as well as the data bus in executing an instruction.So it is called multiplexed bus.It carries the latest significant 8 bit address and data bus.

3-Control and status signal :-

                                             This signal are used to identify the nature of operation. There are three control and status signal.

(i)-Control signal:- 

(a) RD - This signal indicate that the data must be read from the selected memory location or  by I/O port via data bus.

(b) WR - This signal indicates that the data must be written in to selected memory location for I/O port via data bus.

(c) ALE - It is positive going pulse generated when a new operation(machine cycle). It indicates that the bite on AD7-AD0 are address bites.

(ii)-Status signal:- 

(a) IO/M - the signal used to differentiate between IOS and memory operation. When it is high indicates IO operation and when it is low it is indicates memory operation.

(b) S1 & S2 :- This signal indicates the type of machine cycles progress.

4-Power supply and clock frequency - 

(i)-Power supply:-

Vcc - It requires a single 5 volt supply.

Vss - This indicates ground reference.

(ii)-Clock frequency:-

X1 & X2 - A crystal is connected at these two pens. The frequency in internally divided by 2 therefore to operate a system at 3 MHz the crystals should have frequency of 6 MHz

CLK OUT - CLK out or clock out signal can be used as a system clock for other device.

5-Interrupts and externally initiated signals:-

The 8085 has five interrupt signals i.e TRAP, RST 7.5, RST 6.5, RST 5.5 and INTR. We discuss interrupt signals in addition to interrupts, 3 pins RESET,HOLD and READY accept the externally initiated signals as input

INTR (input) -

Interrupt request: This signal is used to general purpose interrupts. It is similar to the signal of 8080A.

INTA(output) -

Interrupt acknowledge: This signal used to you acknowledge an interrupt.

RST7.5, RST 6.5 and RST 5.5 (input) -

Restart interrupts:These are vectored interrupts that transfer the program control to specific memory location. They have higher priorities then the INTR.

TRAP(input) -

This signal is non mistake while interrupt and has a highest priorities.

HOLD(input) -

This signal indicates that are peripheral such as DMA(direct memory access) controller is requesting the use of address and data buses.

HLDA(output) -

Hold acknowledge: the signal acknowledge the hold request.

READY (input) -

The signal used to delete the microprocessor read or write cycle until a slow responding peripheral is ready to send or accept data.

RESET IN -

The signal used to reset the microprocessor coma the program counter is set to be zero.

RESET OUT -

The signal indicates that the MPU is being reset the signal can be used to reset other devices.

6-Serial I/O signals:- 

The 8085 microprocessor has two serial I/O signals these are-

SID (serial input data)-

This input signal is used to accept serial data bit by bit from external device.

SOD(serial output data)-

This is an output signal which enables the transmission of serial data bit by bit to the external device.