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Keyboard Interfacing with 8086 Using 8255: Tips and Tricks (PDF)


Keyboard Interfacing with 8086 Using 8255 PDF 153




Keyboard interfacing is a process of connecting a keyboard to a microprocessor system and enabling the communication between them. Keyboard interfacing can be done in various ways, depending on the type and size of the keyboard, the number of keys, and the desired functionality. In this article, we will focus on keyboard interfacing with 8086 using 8255, a programmable peripheral interface device that can be used for parallel data transfer.




keyboard interfacing with 8086 using 8255 pdf 153



What is 8086?




8086 is a 16-bit microprocessor developed by Intel in 1978. It is the first member of the x86 family of microprocessors, which are widely used in personal computers and other devices. The 8086 has a 20-bit address bus and can access up to 1 MB of memory. It also has a 16-bit data bus and can perform arithmetic and logic operations on 8-bit or 16-bit data. The 8086 has four segments: code, data, stack, and extra, which can be used to organize the memory space. The 8086 has two modes of operation: minimum mode and maximum mode. In minimum mode, the 8086 can operate as a single processor system with minimal external hardware. In maximum mode, the 8086 can operate as a multiprocessor system with additional components such as bus controller and bus arbiter.


What is 8255?




8255 is a programmable peripheral interface device designed by Intel in 1976. It is a general purpose device that can be used for parallel data transfer between the microprocessor and various peripherals. It has 24 I/O pins which can be grouped into three 8-bit ports: Port A, Port B, and Port C. Port C can be further divided into two 4-bit ports: Cupper and Clower. The function and mode of operation of each port can be programmed by writing a control word into the control register of the device. The 8255 can operate in two basic modes: Bit Set/Reset (BSR) mode and I/O mode. In BSR mode, individual bits of Port C can be set or reset by writing a bit pattern into the control register. In I/O mode, each port can operate in one of the three sub-modes: Mode 0, Mode 1, or Mode 2. In Mode 0, each port can function as a simple input or output port without handshaking signals. In Mode 1, each port can function as an input or output port with handshaking signals provided by Port C. In Mode 2, only Port A can function as a bidirectional port with handshaking signals provided by Port C.


How to interface keyboard with 8086 using 8255?




There are different types of keyboards available in the market, such as QWERTY keyboards, matrix keyboards, hexadecimal keyboards, etc. Each keyboard has its own advantages and disadvantages depending on the application and user preference. For simplicity, we will consider a matrix keyboard with 3 rows and 8 columns of keys as an example. A matrix keyboard consists of a grid of switches arranged in rows and columns. Each switch corresponds to a key on the keyboard. When a key is pressed, it closes the switch and connects the corresponding row and column lines. By scanning the row and column lines, we can detect which key is pressed.


To interface a matrix keyboard with 8086 using 8255, we need to connect the row lines to one port (say Port A) and the column lines to another port (say Port B) of the device. We also need to connect some handshaking signals from Port C to enable synchronization between the keyboard and the microprocessor. The following steps describe the procedure for keyboard interfacing:


  • Configure Port A as an output port and Port B as an input port by writing an appropriate control word into the control register of the device.



  • Initialize Port A with all zeros (00000000) to select all rows.



  • Read Port B to check if any column line is low (0). If yes, it means that a key is pressed.



  • If no column line is low (0), go back to step 2.



  • If a column line is low (0), identify which column it is by using a priority encoder or a lookup table.



  • Change Port A to select only one row at a time by making one bit high (1) and others low (0).



  • Read Port B again to check if the same column line is still low (0). If yes, it means that the key belongs to that row.



  • If no column line is low (0), go back to step 6.



  • If a column line is low (0), identify which row it is by using a priority encoder or a lookup table.



  • Combine the row and column information to get the key code of the pressed key.



  • Send an interrupt signal to the microprocessor from Port C to indicate that a key code is available.



  • The microprocessor reads the key code from Port A or Port B depending on how they are connected.



  • The microprocessor processes the key code according to the application logic.



  • The microprocessor sends an acknowledgment signal to Port C to indicate that it has read the key code.



  • The device resets Port A to all zeros (00000000) and waits for another key press.



Conclusion




Keyboard interfacing with 8086 using 8255 is a common task in many microprocessor-based systems that require user input. By using a programmable peripheral interface device such as 8255, we can simplify the hardware design and reduce the number of I/O pins required for keyboard interfacing. We can also program the device to operate in different modes and sub-modes according to our needs. Keyboard interfacing with 8086 using 8255 requires some knowledge of microprocessor programming and logic design. We hope this article has helped you understand how keyboard interfacing with 8086 using 8255 works and how you can implement it in your own projects.


Conclusion




Keyboard interfacing with 8086 using 8255 is a common task in many microprocessor-based systems that require user input. By using a programmable peripheral interface device such as 8255, we can simplify the hardware design and reduce the number of I/O pins required for keyboard interfacing. We can also program the device to operate in different modes and sub-modes according to our needs. Keyboard interfacing with 8086 using 8255 requires some knowledge of microprocessor programming and logic design. We hope this article has helped you understand how keyboard interfacing with 8086 using 8255 works and how you can implement it in your own projects. 4e3182286b


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