Q1

What is the need for using a Schmitt trigger receiver at the reset input from    the push-button to generate the reset pulse to the system.	[2 marks]

Solution: 

To reset the system reliably, reset signal should be active for a specified period. Once manual reset is done, reset will be low for few milli seconds which is sufficient to reliably reset the entire system. As the capacitor charges and reaches just the voltage corresponding to 1, if any, noise is picked up by the signal, it may fluctuate and may give reset for a short duration. As the reset has reached 1 a clock might have started. Under these conditions of clock presence and unreliable reset signals, things might go haywire. If you place a Schmitt trigger then due to hysteresis, noise on the reset line may not affect the reset signal as it might not have crossed the threshold level. This gives the system a reliable operation. Hence Schmitt trigger is highly desirable.


Q2

Connect a 27 pin SRAM organized 8K x 8 to 8085 processor and write a program to check the memory by writing 0’s in all locations and checking them by reading and followed by writing all 1’s and checking the same in all locations. Give a neat circuit diagram and the program. If the checking is successful, put on a green LED and if it is unsuccessful put on a red LED. 	[5 marks]

Solution:

(General Program flow)
Initialize all LEDs
Store all Zeros to RAM
Start reading from RAM
 		If not Zero anywhere
                  Jump to Error Routine
Store all 1s to RAM
	Start Reading from RAM
		If not One anywhere
		  Jump to error routine
	Glow green LED
Error Routine
	Glow Red LED
Halt


(Refer to the link on the course page for the circuit diagram)


Q3 [3 marks]

Explain :

a) Two architectural differences between 8085 and 8086

Solution:

1. 8085 is an 8-bit processor whereas 8086 is a 16 bit processor.  In 8085 the       fetch execute of machine instructions are sequential whereas in 8086, they are      overlapped. 
2. One feature introduced in 8086 which was not there in 8085 is segmentation to       have multiprogramming facility.
3. 8086 has Floating point and I/O Processor support through 8087 & 8089. 


b) Why reset need to be given to 8255.

Solution:

Essentially to make all the ports to act as inputs so that there won’t be any clash of signals on this line. 

c) Main Architectural difference between 8088 and 80188.

Solution:

8088 is a microprocessor whereas 80188 has other units in it and can be classified as a microcontroller. 


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