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Monday, 1 July 2019

Pin Diagram of Intel 8085 Microprocessor

There are 40 pins in Intel 8085 microprocessor. The photo image is shown in figure and pin diagram is shown in figure.

Intel 8085 microprocessor

Pin diagram of Intel 8085 microprocessor
The signals are classified into the following categories.

S.No.
Group
1
Address bus
2
Multiplexed Address / Data bus
3
Control and Status signals
4
Peripheral initiated signals
5
Clock signals
6
Reset signals
7
Interrupt signals
8
Serial I/O signals
9
Power supply and Ground signals

The signal diagram is shown in figure below.
Signal diagram of Intel 8085 microprocessor

Pin number
Signal name
Description
Address Bus
21 – 28
A8 – A15
Higher order byte (8 bits) of address bus. The address bus is unidirectional (one-way, ie. microprocessor to memory).
Multiplexed Address / Data bus
12 -19
AD0 – AD7
Lower order byte (8 bits) address bus (A0 - A7). And Data bus (8 bits) (D0 – D7).The data bus is bidirectional (two-wayie. microprocessor to memory and memory to microprocessor).
Control and Status signals
30
ALE
ALE - Address Latch Enable. Used for de-multiplexing the Address / Data bus. i.e. separating the lower order address lines (A0 – A7) and data lines (D0 – D7) from (AD0 – AD7).
29
S0
The microprocessor indicates its status (memory write, memory read, I/O write, I/O read, Opcode fetch, Halt, Hold, Reset) through these three output pins. IO/M’ will be ‘1’ for I/O operation and ‘0’ for memory operation.
33
S1
34
IO / M' (M - bar)
32
RD’
This is an active low signal. It will be 0 during memory read and I/O read operation.
33
WR’
This is an active low signal. It will be 0 during memory write and I/O write operation.
Peripheral initiated signals
35
READY
This pin is used for interfacing slow devices with the microprocessor.
39
HOLD
DMA (Direct Memory Access) signals:
HOLD (hold request)
HLDA (hold acknowledge)
38
HLDA
Clock signals
1, 2
X1, X2
Used for connecting the crystal for generating the clock signal.
37
CLK OUT
Clock signal for the peripheral devices.
Reset signals
36
RESETIN’
Used to apply reset signal to the microprocessor. When this pin goes low, the microprocessor is reset and begins executing the instruction from the memory location 0000. All the registers inside the microprocessor is reset to zero.
3
RESET OUT
Used to reset the peripheral devices.
Interrupt signals
6
TRAP
Interrupt request input signals to the microprocessor.
7
RST 7.5
Interrupt request input signals to the microprocessor.
8
RST 6.5
9
RST 5.5
10
INTR
11
INTA’
Interrupt Acknowledge signal from the microprocessor to the peripheral devices.
Serial I/O signals
5
SID
Serial Input Data. Used to receive serial data bits.
4
SOD
Serial Output Data. Used to transmit serial data bits.
Power supply and Ground signals
40
VCC
Power supply pins.
+5V to VCC
GND to VSS
20
VSS



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