Test: The Keyboard/Display Controller 8279 - Computer Science Engineering (CSE) MCQ

The control and timing registers store the keyboard and display modes and other operations programmed by CPU.

In this mode, each key code of the pressed key is entered in the order of the entry, and in the meantime, read by the CPU, till the RAM becomes empty.

The display address registers holds the address of the word currently being written or read by the CPU to or from the display RAM.

In scanned keyboard mode with 2 key lockout mode of operation, when a key is pressed, a debounce logic comes into operation. During the next two scans, other keys are checked for closure and if no other key is pressed then the first pressed key is identified.

The scanned keyboard special error mode is programmed using end interrupt/error mode set command. This mode is valid only under the N-key rollover mode.

In this mode, When a key is pressed, the debounce circuit waits for 2 keyboard scans and then checks whether the key is still depressed. If it is still depressed, the code is entered in FIFO RAM.

The data that is entered from the left side of the display unit is of left entry mode, as in a type-writer the first character typed appears at the left-most position, while the subsequent characters appear successively to the right of the first one.

Overrun error occurs, when an already full FIFO is attempted an entry. Underrun error occurs when an empty FIFO read is attempted.

 AI refers to auto increment flag.

 In sensor matrix mode, the IRQ line goes high, if any change in sensor value is detected at the end of a sensor matrix scan or the sensor RAM has a previous entry to be read by the CPU.