Microprocessor 8085 pin description/configuration and classification.

1. DAWOOD UNIVERSITY OF ENGINEERING AND TELECHNOLOGY
DEPARTMENT OF TELECOMMUNICATION ENGINEERING
Microprocessor and Microcontroller System
ONLINE MID EXAMINATION-2020
MICROPROCESSOR 8085 PIN
CONFIGURATION
Presented by:
Mr. Noor Nabi Khan
Roll No:D-19-TE-28
Date:02-09-2020

2. 8085-Pin Diagram
First of all we will have a look at the basic Pin diagram of a 8085:
This diagram basically
describe the architecture
of an 8-bit general
purpose microprocessor
that can address 64Kb of
memory.
The 8085 has 40 pins
and uses the input
voltage of 5V for
power.
This processor can run
or perform at the
maximum frequency of
3 MHz.

3. CLASSIFICATION OF 8085 PINS
The pins of the microprocessor are classified into mainly seven groups
according to the properties of each pin, studying each pin will be complicated
so these pins are grouped to gather which is easier to understand;
1. Address Bus and Data Bus
2. Control and Status Signals
3. Power Supply and Clock Frequency
4. Interrupts
5. Reset Signals
6. External/Peripheral Signals
7. Serial I/O ports

4. 1.Address and Bus Data:
• The group consists of 16 pins which are named from A0 to A15.
• The Address bus from A8 to A15 are unidirectional which means that the bits can
flow only in one direction from 8085 to other peripheral devices. It carries most
significant 8-bits of memory address
• While the Data bus from A0 to A7 are bidirectional which means they can perform
in two directions at a time bit can flow in 2 ways. It carries least significant 8-bit
address and data bus.

5. 2.Control and Status Signals:
The control and status signals have three pins each total of 6 pins. Basically these
pins or signals are used to check the type of the operations that what operation is
going on.
Control Signals: RD,WR and ALE.
• ALE: It stands for Address Latch Enable. It tells us the address if the pulse is high i.e. 1 and it tells
the data when it is low i.e. 0.
• WR: It is signal of control Write operation. Data bus is written when the pulse goes low.
• RD: It is signal of control Read operation. The selected memory will be read when the pulse is low.

6. 3.Power Supply and Clock Frequency:
Power Supply pins are those which are used to give power input to the
processor through different specific ports:
• VCC: It is +5V power supply
• VSS: It is the ground reference.
• Clock Signals pins:
• X1 and X2: the crystals are connected to these two pins. The internal frequency is
divided by two. It is basically used for the clock signal generator.
• CLK (OUT): This signal can be used as the system clock for other peripheral
devices.

7. 4.Interrupts:
These are request signals. 8085 has five interrupts signals that are used
to interrupt the execution of program of command; RST 7.5, RST 6.5,
RST 5.5, TRAP and INTR.
The microprocessor 8085 accepts the requested interrupt
by INTA signal.
• INTR: this is an interrupt request signal from devices.
• INTA: this is an acknowledgment sent by 8085 after
INTR is received.

8. 5.Reset Signals:
RESET IN: when the signal on this pin is low ‘0’ then the counter set the program to zero. Then the
microprocessor is reset.
RESER OUT: after the microprocessor is reset this signal indicates that the unit is reset, and then the
other devices can also be reset now.
6.External or Peripheral Initiated Signals:
In addition to the interrupts and reset signals the 8085 has three external/peripheral initiated signals.
• HOLD: the HOLD tell us that the other external device is requesting to use the address and data bus.
• HLDA: this is basically a acknowledgment that the HOLD request has been received and the access will be
granted in next clock cycle. This goes low(0) after removal of request.
• READY: the READY signal tell us that the device can be used fro transfer data. The system has to wait until
the READY goes high(1).

9. 7.Serial I/O Ports:
The serial transmission lines in 8085 are performed by two signals and these signals
can be used for communication.
• SID: SID is Serial Input Data line. The input data line used for
serial input. The data in this input data line is loaded into accumulator
when instruction is executed.
• SOD: this is Serial Output Data line. This line is used for serial output
and the output is set or reset as specified by the instruction.

10. CONCLUSION

11. THANK YOU