The keyboard first scans the keyboard and identifies if any key has been pressed. It then sends their relative response of the pressed key to the CPU and vice-a-versa. The Keyboard can be interfaced either in the interrupt or the polled mode. In the Interrupt mode , the processor is requested service only if any key is pressed, otherwise the CPU will continue with its main task. In the Polled mode , the CPU periodically reads an internal flag of to check whether any key is pressed or not with key pressure. The keyboard consists of maximum 64 keys, which are interfaced with the CPU by using the key-codes.
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In the encoded mode, a binary count sequence is put on the scan lines SL0-SL3. These lines must be externally decoded to provide the scan lines for keyboard and display.
A 3 to 8 decoder 74LS is provided for this purpose. The S0-S1 output lines of this decoder are connected to the two rows of the keyboard. Pin number 24 to 31 is connected to 7 segments. To initialize and to display the character "A" in the first digit of the display. Then, write the data to be displayed, to the data register.
To read a key and store the key code in memory location This code will be entered into the FIFO whenever a key is pressed. To read a key, procedure to be followed is,. This can be done by checking the least significant 3 bits of the status word. If it zero, it means there is no key closure, so keep checking again. The following program waits for a key to be pressed in the keyboard , reads the same and stores it in the location The initialization of is same as that of Example Then, the data is fetched from address CH and displayed in the first digit of the display.
The next data is displayed in the second Digit of the display, since in the command word for 'write display RAM' the Auto Increment flag is set. A time delay is given between successive digits for a lively display. To accept a key from the Hex keyboard and display it in the display. A lookup table is provided to obtain the corresponding display codes for the keys. Click here to Download.
Product Description Introduction of Keyboard and Display Keyboard and Display controller card designed to study the features of keyboard and Display controller PS- Interface card consist of 6 Nos. Submit Review. From Decoder. RST 5.
8279 - Programmable Keyboard
Selects the number of display positions, type of key scan Programs internal clk, sets scan and debounce times. Selects type of FIFO read and address of the read. Selects type of display read and address of the read.