Two Marks Questions with Answers

Two Marks Questions with Answers

 

Q.1 Define scan counter.

Ans. : The scan counter has two modes to scan the key matrix and refresh the display. In the encoded mode, the counter provides binary count that is to be externally decoded to provide the scan lines for keyboard and display. In the decoded scan mode, the counter internally decodes the least significant 2 bits and provides a decoded 1 out of 4 scan on SL0-SL3. The keyboard and display both are in the same mode at a time.

 

Q.2 What is the output modes used in 8279 ?

Ans. : 8279 provides two output modes for selecting the display options.

1. Display scan : In this mode, 8279 provides 8 or 16 character-multiplexed displays those can be organized as dual 4-bit or single 8-bit display units.

2. Display entry : 8279 allows options for data entry on the displays. The display data is entered for display from the right side or from the left side.

 

Q.3 What are the modes used in keyboard modes ?

Ans. : 1. Scanned keyboard mode with 2-key lockout. 2. Scanned keyboard with N-key rollover. 3. Scanned keyboard special error mode. 4. Sensor matrix mode.

 

Q.4 What are the modes used in display modes ?

Ans. : 1. Left entry mode : In the left entry mode, the data is entered from the left side of the display unit.

2. Right entry mode : In the right entry mode, the first entry to be displayed is entered on the rightmost display.

 

Q.5 what is 8279 ?

Ans. : The 8279 is a programmable keyboard/display interface.

 

Q.6 List the major components of the keyboard/display interface.

Ans. : a. Keyboard section b. Scan section c. Display section d. CPU interface section

 

Q.7 What is key bouncing ?

Ans. : Mechanical switches are used as keys in most of the keyboards. When a key is pressed the contact bounce back and forth and settle down only after a small time delay (about 10 ms). Even though a key is actuated once, it will appear to have been actuated several times. This problem is called key bouncing.

 

Q.8 How much current is needed to drive an LED ? Draw a typical driver circuit for it. 

Ans. : Around 15 mA current is needed to drive LED. The typical driver circuit for LED is

 

Q.9 How keyboard debouncing is done by software ?

Ans. : In the software technique, when a key press is found, the microprocessor waits for at least 10 ms before it accepts the key as an input. This 10 ms period is sufficient to settle key at steady state. In this way key debouncing is done by software.

 

Q.10 What is the difference between two key lockout and N-key rollover modes in 8279 ?

Ans. : 2-key lockout : In this mode, simultaneous key depression is not allowed.

N-key rollover : In N-key rollover, each key depression is treated independently from all others.

 

Q.11 List the functions performed by 8279.

Ans. : The functions performed by 8279 are :

1. It independently keeps display refresh with its multiplexed display interface in right entry mode or left entry mode.

2. It scans the matrix keyboard upto 64 keys with three input modes : scanned keyboard mode, scanned sensor matrix mode and stored input mode.

 

Q.12 What is the internal operating frequency of 8279 ? How can you derive it from any available clock signal ?

Ans. : The internal operating frequency of 8279 is 100 kHz. We can derive the internal operating frequency from any available clock signal using internal prescaler.

This prescaler divides the external clock by a programmable integer value given in the program clock command word, to generate internal frequency.

 

Q.13 Describe the three major tasks needed to get meaningful information from matrix keyboard.

Ans. : 1. Initialize keyboard in proper mode.

2. Initialize prescaler count.

3. Read keyboard entry from FIFO RAM.

 

Q.14 What is the necessity for a separate 8279 keyboard display controller ?

Ans. : In software approach, to drive multiplexed displays CPU has to look after digit selection in synchronism with the data for specific digit and these displays need continuous refreshing. This puts a lot of burden on the CPU. In keyboard interface to provide facilities such as 2-key lockout, N-key Rollover CPU needs to execute necessary programs which further increases the burden on CPU and hence it is necessary to have separate 8279 keyboard/display controller.

 

Q.15 What is the function of scan section in 8279 programmable keyboard/display controller ?

(Refer section 12.5.2)

Q.16 What is keyboard interfacing ?

(Refer section 12.1)

 

 

University Questions with Answers (Long Answered Questions)

 

(Regulation 2008)

Dec.-11

Q.1 Explain the operation of the keyboard/display controller with a neat diagram. (Refer section 12.5)         [8]

Dec.-12

Q.2 List the major components of the 8279 keyboard / display interface and explain their functions in detail. (Refer section 13.5)      [8]

May-13

Q.3 Draw and explain the functional block diagram of 8279 keyboard display controller. (Refer section 13.5)         [8]

Dec.-13

Q.4 Explain features of 8279 keyboard/display controller. (Refer section 13.3)   [8]

Q.5 Draw and explain the architecture of 8279 keyboard I display controller. (Refer section 13.5) [8]

Dec.-14

Q.6 Explain about 8279 keyboard display controller in detail. (Refer section 13.3)      [16]

(Regulation 2013)

Dec.-15

Q.7 Explain the block diagram, architecture and registers of the 8279 keyboard / display Controller. (Refer section 13.5)        [16]

May-16

Q.8 With neat diagram, explain the architecture and features of 8279 keyboard display controller. (Refer sections 13.3 and 13.5)  [16]

Dec.-16

Q.9 Explain the working of 8279 as a keyboard/display controller and explain its command registers and their functions. (Refer sections 13.6 and 13.7)   [16]

Dec.-17

Q.10 With a neat diagram, explain the internal architecture of keyboard and display controller IC - 8279. (Refer section 13.5)         [13]

May-18

Q.11 Design an 8085 based system with 512B RAM., 4KB ROM, external keyboard and seven segment display device. (Refer sections 6.4.1, 13.1 and 13.2) [15]