memory mapped I/O- DMA-operation of 8255-cascaded mode of 8259-lockout and N- key rollover modes in 8279-8279 controller-stepper motor-peripheral ICs-Programmable interval Timer / Counter IC

1.List the features of memory mapped I/O.

(i) A maximum number of I/O devices are 1 Mbyte.
(ii) Requires decoding of 20 address lines and hence more hardware involved.

2.What are the basic modes of operation of 8255?

There are two basic modes of operation of 8255. They are:
(i) I/O mode
(ii) BSR mode

3.How to change the direction of the stepper motor from clockwise direction to anticlockwise direction using a program segment?

By reversing step sequence (excitation code sequence) it is possible to change the direction of rotation of the stepper motor.

3. A.4.Name the peripheral ICs used for parallel and serial data transfer.

8255 and 8251.

5.What are the advantages of Programmable interval Timer / Counter IC ?

(i)The 8253/8254 includes three identical 16-bit counters that can operate independently.
(ii)The 8254 is a superset of 8253.

3. A.6.What is the function of scan section in 8279 controllers?

(i) Encoded scan- Scan lines are decoded externally to provide 8 scan lines.
(ii) Decoded scan- internal decoder decodes and provides 4 scan lines.

7.What is the cascaded mode of 8259 programmable interrupt controller?

The mode in which 8259s are interconnected to get multiple interrupts is called cascaded mode.

8.What is DMA?

A special control unit may be provided to enable transfer a block of data directly between an external device and memory without continuous intervention by the CPU. This approach is called DMA (Direct Memory Access).

9.State the advantages of DMA.

(i) The data transfer is very fast.
(ii) The processor is not involved in the data transfer operation and hence it is free to execute other tasks.

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

2-Key lockout: Simultaneous key depression is not allowed.

N-key rollover: Each key depression is treated independently from all others. 

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