The document describes the architecture and pin configuration of the Intel 8085 microprocessor. It has the following key components: - A processor, memory, input, and output units. It communicates using address, data, and control buses. - A 40-pin IC with pins for power supply, crystal clock input, multiplexed address/data bus, control signals, interrupts, serial I/O and reset functions. - It operates at 3MHz clock speed from a 6MHz crystal input. The address bus is 16-bits wide while data is 8-bits wide. - The pins have various functions like memory/I/O selection, read/write control, interrupt requests and acknowledgements

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3. • A microprocessor is a multipurpose,
programmable, clock – driven, register based
electronic device.
• It consists of four basic parts:
• Processor
• Memory
• Input
• Output
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7. • Address Bus
• Data Bus
• Control Bus
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8. • Machine Language
• Assembly Language
• High Level Languages
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9. An 8 – bit processor
Having
A 16 – bit Address Bus
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10. ARCHITECTURE OPERATIONS
• ALU
• Register
Array
• Control Unit
• System Bus
• Opcode Fetch
• Memory Read
• Memory Write
• Input Read
• Output Read
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11. Accumulator Flag Register
B C
D E
H L
Stack Pointer (SP)
Program Counter (PC)
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12. X1 1 40 VCC
X2 2 39 HOLD
RESET OUT 3 38 HLDA
SOD 4 37 CLK (OUT)
SID 5 36
TRAP 6 35 READY
RST 7.5 7 34 IO/
RST 6.5 8 33 S1
RST 5.5 9 32
INTR 10 31
11 30 ALE
AD0 12 29 S0
AD1 13 28 A15
AD2 14 27 A14
AD3 15 26 A13
AD4 16 25 A12
AD5 17 24 A11
AD6 18 23 A10
AD7 19 22 A9
VSS 20 21 A8
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13. • Intel 8085 is a 40 – pin IC.
• The various signals on these pins can be
classified into six groups:
o Address Bus
o Data Bus
o Control and Status signals
o Externally Initiated signals
o Serial I/O ports
o Power Supply and Frequency signals
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14. Pin No. 40 – VCC
Pin No. 20 – VSS
Pin No. 01 – X1
Pin No. 02 – X2
Pin No. 37 – CLK (OUT)
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15. • VCC & VSS are the power supply pins.
• X1 and X2 are the crystal clocks.
 Each having a frequency of 6 MHz.
 The frequency is internally divided by two.
 So the system works at a frequency of 3 MHZ.
• CLK (OUT) is Clock Out.
 It is used to give system clock to other devices.
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16. Pin No. (12 – 19) – AD0 – AD7
Pin No. (21 – 28) – A8 – A15
AD0 – AD7 – Multiplexed Address/Data Bus
 Pin no. 12 – 19 are the multiplexed pins.
 They serve the purpose of address bus as well as data bus.
 As address bus, they serve as, lower order address bus.
A8 – A15 – Address Bus
 Pin no. 21 – 28, serve as, higher order address bus.
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17. Pin No. 29 & 33 – S0 & S1
Pin No. 30 – ALE
Pin No. 31 -
Pin No. 30 -
Pin No. 30 – IO/
WR
RD
M
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18. S0 & S1 – are the status signals.
 to identify various microprocessor operations.
ALE – Address Latch Enable
 It is a control signal.
 It is used to demultiplex the address/data
bus.
It is a control signal
 to initiate the write operation.
WR
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19. - It is a control signal
 to initiate the operation.
IO/ - It is a control signal
 to activate memory/IO buffer.
RD
M
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20. Pin No. 3 – RESET OUT
Pin No. 6 - TRAP
Pin No. 7 – RST 7.5
Pin No. 8 – RST 6.5
Pin No. 9 – RST 5.5
Pin No. 10 - INTR
Pin No. 11 -
Pin No. 35 - READY
Pin No. 36 -
Pin No. 38 - HLDA
Pin No. 39 - HOLD
INTA
RESETIN
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21. TRAP, RST 7.5, RST 6.5, RST5.5 & INTR
 Are five interrupts on 8085 chip, with
 TRAP having highest priority, and
 INTR having lowest priority
 Except INTR, all the other four interrupts are vectored.
 Only INTR is non-vectored interrupt.
- is interrupt acknowledgement.
 This signal is initiated by the processor, to respond to
an interrupting device.
INTA
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22. HOLD – This signal is used by a peripheral to
request the processor to gain control
over the system bus.
HLDA – This signal is initiated by the
microprocessor, in response to HOLD
signal.
READY – Signal on this pin is sent by a slow
responding peripheral, in order to delay the
microprocessor
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23. - When the signal on this pin goes low,
the processor is reset.
RESET OUT – This signal s used to reset other
devices, when microprocessor is
being reset.
RESETIN
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24. Pin No. 4 – SOD
Pin No. 5 – SID
There are only two pins under this category –
SID – Serial Input Data
SOD – Serial Output Data
These pins are used for serial input/output data
transmission.
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