External Architecture of 8085 Microprocessor

1. Introduction

• 8085 is an 8-bit microprocessor.
• The data bus size is 8 bits and the address bus size is 16 bits.
• There are a total of 40 pins.

2. Significance of Pins

2.1 Data and Address Bus

• A8 to A15 Pins: For address bus.
• AD0 to AD7 Pins: A mixture of address and data.

2.2 ALE (Address Latch Enable)

• It helps determine whether to use the pin for address or data.
• When the value of ALE is 1, the pins are for the address.
• When the value of ALE is 0, the pins are for data.

2.3 I/O and M Pin

• I/O Pin: If the value is 1, input-output devices are enabled.
• If the value is 0, memory is used.

2.4 RD and WR Pins

• RD (Read): To read from memory or device.
• WR (Write): To write into memory or device.
• Low enabled pins mean when the value is 0, the pins are enabled.

2.5 S1 and S2 Pins

• These are status pins indicating whether memory is being read from or written to.

3. Interrupts

3.1 TRAP

• The highest priority interrupt.
• Related to hardware emergencies like power failure.

3.2 RST Pin

• For different software interrupts.

4. DMA (Direct Memory Access)

• Hold and Hold Acknowledgment: Connected via DMA controller.
• Allows the microprocessor to transfer data between memory and input-output devices.

5. Reset Pins

• Reset In: To reset the microprocessor.
• Reset Out: To reset external devices.

6. READY Pin

• Indicates that peripheral devices are ready.

7. SID and SOD

• SID: Serial input.
• SOD: Serial output.

8. Other Pins

• VCC: 5 Volts.
• VSS: Ground connection.
• X1 and X2: Clock signal.

9. Conclusion

• Understanding the implementation of 40 pins in the 8085 microprocessor is important.
• It is useful information for competitive exams.

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Thank you!