Interrupts are the signals generated by external devices to request the microprocessor to perform a task. There are 5 interrupt signals, i.e. TRAP, RST 7.5, RST 6.5, RST 5.5, and INTR. We will discuss interrupts in detail in interrupts section.

8085 microprocer is used to Addition supration multiplication divisition and used to calculate polinomial equation.The pins of a 8085 microprocessor can be classified into seven groups −
Address bus
A15-A8, it carries the most significant 8-bits of memory/IO address.
Data bus
AD7-AD0, it carries the least significant 8-bit address and data bus.
Control and status signals
These signals are used to identify the nature of operation. There are 3 control signal and 3 status signals.
Three control signals are RD, WR & ALE.
• RD − This signal indicates that the selected IO or memory device is to be read and is ready for accepting data available on the data bus.
• WR − this signal indicates that the data on the data bus is to be written into a selected memory or IO location.
• ALE − It is a positive going pulse generated when a new operation is started by the microprocessor. When the pulse goes high, it indicates address. When the pulse goes down it indicates data.

1. Presented By
Siddhesh S. Palkar
Pin Diagram 8085 &
Features of 8085

2. Features of 8085
It is an 8 bit processor
Itis a single chip N-MOS device with 40 pins.
Ithas multiplexed address and data bus(AD0 -AD7)
It works on 5 Volt DC power supply
The maximum clock frequency is 3 MHz while
minimum frequency is 500 KHz.
Itprovides 74 instruction with 5 different addressing
modes.

3. Pin Diagram

4. Address Bus
These pins carry the
higher order of address
bus.
The address is sent from
microprocessor to
memory.
A8 –A15. It carries the
most significant 8-bit of
memory I/O address.

5. Data Bus
Data bus is of 8 Bit.
It is used to transfer
data between
microprocessor and
memory.
AD0–AD7. It carries the
least significant 8-bit
address and data bus.

6. Control Signals
RD
Thissignalindicatesthat
theselectedIOormemory
deviceistobereadandis
readyforacceptingdata
availableonthedatabus.
WR
Thissignalindicatesthat
thedataonthedatabusisto
bewrittenintoaselected
memoryorIOlocation.

7. Status Signals
IO/M
Thissignalisusedto
differentiatebetweenIOand
Memoryoperations,i.e.whenit
ishighindicatesIOoperation
andwhenitislowthenit
indicatesmemoryoperation.
S0& S1
Thesesignalsareused
toidentifythetypeofcurrent
operation.

8. Power Supply
There are 2 power
Supply signals:
VCC
VCC indicates +5v power
supply.
VSS
VSS indicates ground signal.

9. Interrupt Signals
TRAP
TRAP is usually used for power failure
and emergency shutoff.
RST 7.5
It is a maskable interrupt. It has the
second highest priority.
RST 6.5
It is a maskable interrupt. It has the
third highest priority.
RST 5.5
It is a maskable interrupt. It has the
fourth highest priority.
INTR
It is a general purpose interrupt. It is a
maskable interrupt. It has the lowest
priority.

10. Externally Initiated Signals
INTA
It is an interrupt acknowledgment
signal.
RESET IN
Thissignalisusedtoresetthe
microprocessorbysettingthe
programcountertozero.
RESET OUT
Thissignalisusedtoresetallthe
connecteddeviceswhenthe
microprocessorisreset.

11. Externally Initiated Signals
Ready
Thissignalindicatesthatthedevice
isreadytosendorreceivedata.If
READYislow,thentheCPUhasto
waitforREADYtogohigh.
HOLD
Thissignalindicatesthatanother
masterisrequestingtheuseofthe
addressanddatabuses.
HLDA
ItindicatesthattheCPUhas
receivedtheHOLDrequestanditwill
relinquishthebusinthenextclock
cycle.

12. Serial I/O Signals
SOD
(Serial Output Data line)
TheoutputSODisset/resetas
specifiedbytheSIMinstruction.
SID
(Serial Input Data line)
Thedataonthislineisloaded
intoaccumulatorwheneveraRIM
instructionisexecuted.

13. Clock signals
X1, X2
Acrystal(RC,LCN/W)is
connectedatthesetwopinsand
isusedtosetfrequencyofthe
internalclockgenerator.This
frequencyisinternallydividedby
2.
CLK OUT
Thissignalisusedasthesystem
clockfordevicesconnectedwith
themicroprocessor.

14. Thank You