hi to all I want to interface a keyboard (preferrably an AT type) to or z80 microprocessor. connection is serial and i might use an interface. Keyboard Interfacing With Using Pdf ->>->>->> DOWNLOAD ( Mirror #1). 1 / 3 . Keyboard,,,Interfacin g,,,With,, . Microprocessor,,,, interfaci. Microprocessor – Programmable Keyboard – Learn Microprocessor in simple and Instruction Sets, Interrupts, Addressing Modes, Multiprocessor Configuration How Many Ways the Keyboard is Interfaced with the CPU?.

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This section describes the characteristics of the based microcomputer used with a hexadecimal keyboard and a seven-segment display. A common method of entering programs into a microcomputer is via a keyboard. A popular way of displaying results by the microcomputer is by using seven-segment displays.

The main functions to be performed for interfacing a keyboard are: Let us now elaborate on keyboard interfacing concepts. A keyboard is arranged in rows and columns. If so, the rows can be.

The row and wifh code for the pressed key can thus be found. The next step is to debounce the key. Key bounce occurs when a key is pressed or released-it bounces for a short time before making the contact. When this bounce occurs, it may appear to the microcomputer that the same key has been actuated several times instead of just once.

8279 – Programmable Keyboard

This problem can be eliminated by reading the keyboard after about 20 ms and then verifying to see if it is still down. If it is, then the key actuation is valid. The next step is to translate the row and column code into a more popular code such as hexadecimal or ASCII.

This can easily be accomplished by a program. Certain characteristics associated with keyboard actuations must be considered while interfacing to a microcomputer. Typically, these are two-key lockout and N-key rollover. The two-key lockout ensures that only one key is pressed. An additional key depressed and released does not generate any codes. The system is simple to implement and most often used.

However, it might slow down the typing because each key must be fully released before the next one is pressed down. On the other hand, the N-key rollover will ignore all keys pressed until only one remains down.

Now let us elaborate on the interfacing characteristics of typical displays. The following functions are typically performed for displays: Output the code via right entry or left entry into the displays if there are more than one displays.

These functions can easily be realized by a microcomputer program. If there are more than one display, the displays are typically arranged in rows. A row of four displays is shown in Figure 9. In the figure, one has the option of outputting the display code via right entry or left entry.


If the code is entered via right entry, the code for the least significant digit of the four-digit display should be output first, then the next digit code, and so on. The program outputs to the displays are so fast that visually all four digits will appear on the display simultaneously.

If the displays are entered via left entry, then the most significant digit must be output first and the rest of the sequence is similar to the right entry. Two techniques are typically used to interface a hexadecimal display to the microcomputer: BCD to seven-segment conversion is done in software. The microcomputer can be programmed to output to the two display digits in sequence. However, the microcomputer executes the display instruction sequence so fast that the displays appear to the human eye at the same time.

In the multiplexing scheme, appropriate seven-segment code is sent to the desired displays on. However, the display to be illuminated is grounded.

Microprocessor – Programmable Keyboard

In this case, the microcomputer is required to output four bits decimal to a display. The keyboard and display interfacing concepts described here can be realized by either software or hardware.

80866 chips are typically initialized by the microprocessor. However, these functions are usually shared between the controller chip and the microprocessor. In this section, an based microcomputer is designed to display a hexadecimal digit entered via a keypad 16 keys.

Port A is configured as an input port to receive the row-column code. Port B is configured as an output port to display interfaving key s pressed.

Port Cis configured as an output port to output zeros to the rows to detect a key actuation. The system is designed interfacung run at 2 MHz. Debouncing is provided to avoid unwanted oscillation caused by the opening and closing of the key contacts. To ensure stability for the input signal, a delay of 20 ms is used for debouncing the input.

The program begins by performing all necessary initializations. Next, it makes sure that all the keys are opened not pressed.

A delay loop of 20 ms is included for debouncing, and the following instruction sequence is used Section 9. The next three lines detect a key closure. If a key closure is detected, it is debounced. It is necessary to determine exactly which key is pressed. The row-column code is input via port A to determine if the column interfacinb changes corresponding to each different row code. If the column code is not OFH changedthe input key is identified.


The program then indexes through a look-up table to determine the row-column code saved in DL. If the code is found, the corresponding index value, which equals the input. The program is written such that it will continuously scan for input key and update the display for each interfacig input.

Note that lowercase letters are used to represent the registers in the program. A listing of the assembly language program is given in the following: In the program, the “Key-open” loop ensures that no keys are closed.

On the other hand, the “Key-close” waits in the loop for a key actuation. Note that in this program, the table for the codes for the hexadecimal numbers 0 through F are obtained by inspecting Figure 9. For example, consider key F. This will make the content of port A as: Thus, a code of is obtained at Port A when the key F is pressed. Diodes are connected at the four bits Bits of Port C.

This is done to make sure that when a 0 is output by the program to one of these bits row of the keyboardthe microrpocessor switch will close and will generate a LOW on that row. This will enable the programmer to obtain the appropriate key code for each key. Sense a key actuation. Share to Twitter Share to Facebook.

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