Generation of Control Signals of 8085

Generation of Control Signals 

In any system, there are different modes of operations. Likewise, in some situation we are interested to read data in microprocessor, in other we are interested to write data on some location from microprocessor. Whenever, we are dealing with different peripherals using 8085 microprocessor there are two modes of operations. One is to read data from any of the memory device or input device. Second is to write data on some location, this location can be any of the output device location or any of the memory location. To deal with these modes 8085 microprocessor architecture gives three different control signals. Namely IO/M,RD and WR. The IO/M is an output pin of the 8085 microprocessor which serves dual purpose, the high going pulse on this pin indicates the I/O type of operation. We can state that, at this time 8085 is working with the input or output devices. The low going pulse on this pin indicates the memory operation. The second one is the RD stand for read signal. This is active low signal, indicates the memory or I/O type of read operation and the selected memory or I/O device is to be read. And the third is WR stands for write signal. This is also active low signal, indicates the memory or I/O type of write operation and data available on the Data bus is to be written in to the selected memory or I/O location, data is set up at the trailing edge of the pin. To deal with different I/O as well as memory device individually, we have to generate four individual control signals. This control signals used to select any of the I/O or memory device, with a specific type of operation either of read or write. In our case, we are interested with two operation with memory as well as output devices. First of all, we required to fetch the instructions place inside the memory and next we write data word on output port. According to our need we have develop the logic to generate control signals. The figure describe the combination logic of signal generation.

Figure: - Example of the schematic Diagram to generate control signals

Figure: - The combination of control signals as well as de-multiplexing the bus system 

REFERENCES

1. R. S. Gaonkar, Microprocessor Architecture, Programming, and Applications with the 8085, Fifth Edition, Penram International Publishing (India) Private Limited.
2. S Ghoshal, Microprocessor Based System Design, Macmillan India Limited, 1996
3. M. Mano, Digital Logic and Computer Design, Prentice – Hall India
4. B. Ram - Fundamentals of Microprocessor and Microcontrollers
5. “Microprocessors: Principles and Applications” by A Pal
6. “Microprocessors and Microcontrollers : Architecture, Programming and Interfacing Using 8085, 8086 and 8051” by Soumitra Kumar Mandal
7. “Introduction to Microprocessors and Microcontrollers” by Crisp John Crisp
8. “Microprocessors And Microcontrollers” by A Nagoor Kani
9. “Microprocessors And Microcontrollers : Architecture, Programming and System Design 8085, 8086, 8051, 8096” by KRISHNA KANT
10. “8 - Bit Microprocessor” by Vibhute