Model Answer, Statistics and Verdict of Mid Semester Exam

Dr A Sahu

Dept of Comp Sc & Engg.

IIT Guwahati

Outline

• Very Easy
• Question 1
• Easy
• Question 2
• OK, If u have read the book/slide
• Question 4
• Question 5
• A Bit difficult one
• Question 3 : Two IC 8255, 8254, 3x2 7SegLED, Binary to BCD conversion

Question No 1

• [10] Answers the following short questions:
• [2] What is memory mapped I/O and IO mapped IO. Explain data movements (instruction and addressing) from IO to CPU and addressing methods in both the cases?
• In I/O mapped IO: addresses are 8 bit, IO can be performed by IN, OUT instruction, Higher address are same as lower address
• In memory mapped IO: addresses are 16 bit, IO can be performed by LD, ST instruction, MOV M R, MOV R M

​

​

​

Question No 1

• [10] Answers the following short questions:
• [1.5] What are different conditions to satisfy for data transfer form CPU to I/O or vice versa?
• Unconditional, status check, polling, interrupt, Interrupt, Ready signal, Handshake-DMA(hold signal),…Answer is in questions itself
• [1.5]What is difference between Status check, Polling and interrupt?
• Polling and Status check are same.. Periodically Check/Poll the device ready/finish status and run take the action if status is Ok..There is diff between ready signal based (MPU check its own bit/pin, device updates to MPU ready bits) and polling (MPU check the device ready signal).
• Interrupt : MPU do its own work, Device interrupt the MPU when it is ready and ISR is executed when it receive an intr.

​

​

Question No 1

• [10] Answers the following short questions:
• [2] Explain steps in transferring data from Memory to IO using DMA controller using HOLD & HLODA.
• HOLD: DMA to CPU
• DMA Send HOLD High to CPU
• I (DMA) want BUS Cycles
• HOLDA
• CPU send HOLDA
• BUS is granted to DMA to do the transfer
• DMA is from Slaves to Master mode
• HOLD Low to CPU
• I (DMA) finished the transfer
• Cycle Stealing if One BUS

Question No 1

• [10] Answers the following short questions:
• [3] What algorithms/methodologies are used for Analog to Digital conversion?
• Counter or Tracking ADC, Successive Approximation ADC (Most Commonly Used), Parallel/Flash ADC (Fast Conversion)
• What are different performance characteristics measures of DAC?
• Resolution, Reference Voltages, Settling Time, Linearity, Speed, Errors

​

​

Question No :2

• Suppose a graphics display having resolution 1600x1200 (1.9MegaPixel) with Frame buffer containing YUV values instead of RGB color values. The human eye has fairly little color sensitivity: the accuracy of the brightness information of the luminance channel (Y) has far more impact on the image discerned than that of the other two (U and V). In case of RGB we store 24 (8+8+8) bits per pixel in frame buffer , but in YUV case we store 4x8+8+8=48 bits for group of 4 pixels ( that is 4 Y values 8 bit each + 1 U value of 8 bit + 1 V value of 8 bit for group of 4 adjacent pixels ). The RGB values can be computed from YUG values by a decoder to render the screen. (Assume YUG to RGB decoder is a black box, you don’t require to draw the internal and you can use 4 such decoder).

​

Design a circuit block diagram to refresh the above designed graphics screen at 30frame/S. What should be Clock values for the both row and column counter to perform at this rate? What should be maximum delay of such YUV to RGB decoder?

​

​

Model Answer to question 2

• YUG coding instead of RGB, 4 Adjacent pixel (two row & 2 col)
• Store Y U,V in different Array
• Use same Col-Row counter, access U, V by (r/2,c/2) and but access Y by (r,c)

0

1

2

3

4

5

1

2

3

0 1 2

0

​

1

R.CTR

C.CTR

Y1

Y2

Y3

Y4

U

V

Model Answer to question 2

• YUG coding instead of RGB, 4 Adjacent pixel (two row & 2 col)
• Store Y1,Y2,Y3,Y4,U,V of Group in a single address
• Effective row and column
• 1600/2=800 rows, 1200/2=600 rows
• Render (rx2,cx2), (rx2,cx2+1), (rx2+1,cx2), (rx2+1, cx2+1)

​

0

1

2

3

4

5

1

2

3

0 1 2

0

​

1

• Use Shift register for

Multiplication

• Last bit flipper for

addition

Clock and Decoder Delay

• 30F/S, 1.9MP
• Clock Speed=(30x1.9x10⁶)=57.6MHz
• YUV to RGB Decoder speed >=1/30x1.9x10⁶ =1.736x10^-8S
• Use of 4 decoder: Speed can be reduced to

(1.736/4)*10^-8S

Question 4

[10] Design interface and write interface program to interface seven I/Os devices namely Emergency actions, A/D converter, Heater, Keyboard, Display, Special money transaction device and printer using 8259 interrupt controller. Design interface the circuit to work at address 80H for ICW1 and 81H for ICW2. Special money transaction device have lower priority then Emergency actions. You have to ensure that Special money transaction device should not be interrupted once its ISR started till the end of its ISR using mask bit. Assume interrupt vector address for each interrupts and use properly in your interface program.

Determine the values of ICWs, OCWs in this case for your interface structure. Draw the interface diagram and write interfacing (8085 assembly) program (to initialize ICWs & OCWs) to perform this work.

​

Example: Setting of control word

8259

IR0

​

IR1

​

IR2

​

​

​

​

​

IR6

Emergency

​

Spe. MoneyT

​

A/DC

Keyboard

Monitor

Heater

​

​

Printer

3-to-8

Decoder

CS^b

​

A₀

E1^b E2^b E3

A₂

A₁

A₀

A₃

A₂

A₁

A₇

A₆

A₅

A₀

OCW1=FDH

ADDRESS= 80H, 81H

0₄

Initialization words (ICW1 & ICW2)

76H

20H

Program to initialize

DI

MVI A, 76H ;move ICW1 byte to ACC

OUT 80H ; initialize 8259A ICW1

MVI A, 20H ; Mov ICW2 byte to ACC

OUT 81H ; Initialize 8259A ICW2

​

MVI A, FDH ; Put the OCW1

OUT 80H

​

Question 5

• [10] Interface a LCD monitor via RS-232 port using a 8251 USART controller. Design the interface diagram so that you should be able to address the SUART at 5EH and 5FH for data and control respectively. Specify initialization instructions and status word to transmit characters with Async mode with 9600 baud rate, 8 bit character length, 2 stop bits and without any parity check.

​

• Write instructions to initialize USART and read status word and setup a loop until the USART transmitter is ready. Using this write an interface program that will send 10 characters from memory to LCD monitor for display.

​

Interface : For Address 5FH & 5EH

8251A

TxD

​

RxD

RxC^b

TxC^b

CLK

CTS^b GND

8085

MPU

D7

​

​

​

D0

CS^b

​

C/D^b

A7

A1

A0

Voltage Converter

IOR^b

IOW^b

Reset Out

CLK Out

RD^b

WR^b

RESET

CLK

D7

​

​

​

D0

Control & Status Register Address=5FH

​

C/D^b line should be high, == > A₀ =1

Initialization of UART: 9600baud, 8 bit char , 2 stop bit, WO parity

Mode

Word

COMMAND WORD

STATUS

CEH

11H

01H

Initialization instructions

SETUP: MVI A,CEH ; load mode word

OUT 5FH ;Write mode word in control register

MVI A,11H ; load command word to enable TX

OUT 5FH ;Enable the transmitter

STATUS: IN 5FH ; Read the status register

ANI 01H ; Mask all bit except D0

JZ STATUS ; if D0=0 the TX buffer if full

Write a program to display message at CRT terminal

LXI H 2070H ; Meory ptr for Message

MOV C, M ; Set up Ctr register

MVI A,40; Reset 8251

OUT 5FH

MVI A,CEH; Initialize 8251

OUT 5FH

MVI A,11 ; initialize for transmit

OUT 5FH

STATUS: IN 5FH

ANI 01H ;Ckeck TxRDY

JZ STATUS ; is txRDY 1 ? If not wait

INX H ; Pont to Next Char

MOV A,M ; place the Char in ACC

OUT 5EH ; Send the Char to Transmitter

DCR C ; DCr cnt

JNZ STATUS ;Again Send the rest of Char

HLT

Question 3

• [10] Design a real time clock with hours, minute and second with 6 seven segment LED display. Interface an 8254 PIT and a group of 6 seven segment LEDS using an 8255 PPC to 8085 microprocessor. Generate 1 Second clock pulse using two counter (ctr0 & ctr1) of 8254PIT and one counter (12hr.60min.60Sec=43200 < max of 16 bit number 65368) for real time clock (ctr2). After every 1 second (generate interrupt to read) read the RTC counter value and format the value in proper format (BCDs HH:MM:SS) and send to output port using 8255.
• Draw the interface diagram and write interfacing (8085 assembly) program to perform this work.

8254 Block Diagram

A7

A6

A5

A4

A3

A2

​

A1

A0

INTR

70

71

72

73

Write a SR to generate an interrupt every 1 Second

• Assume Clock Freq=2MhZ
• Count is too large
• Counter 1 load with 50,000 to generate 25ms
• CNTLOAD=50,000₁₀=C350H
• Counter 2 load with 40 to generate 25msX40=-1S pulse (CNTLOAD=40₁₀=28H)
• CNT3Load = 12x60x60=43200₁₀=A8C0H
• Counter1 output is to counter 2
• Counter2 output is to counter 3
• All Counter 1, Counter 2 & Counter 3 in Mode 2

Instruction to set up 1s interrupt

MVI A , 74H ; Mode for 1^st CTR

OUT 73H ;Write in control register

MVI A,94H ; Mode for 2^nd CTR

OUT 73H ; Write to control register

MVI A,F4H ; Mode for 3^nd CTR

OUT 73H ; Write to control register

​

MVI A,50 ; low byte of CTR1=C350

OUT 70H ; load to CTR1 low byte

MVI A,C3 ; high byte of CTR1=C350

OUT 70H ; load to CTR1 high byte

​

MVI A,28H ; Count for Counter 2

OUT 71H ; Load Counter 2

​

MVI A,C0 ; low byte of CTR3=A8C0H

OUT 72H ; load to CTR1 low byte

MVI A,A8 ; high byte of CTR3=A8C0H

OUT 72H ; load to CTR1 high byte

Control word

• Counter 1 (74H)

​

​

• Counter 2 (94H)

​

​

• Counter 3 (F4H)

Require 8255

• Port A : Output (Sec)
• Port B: Out put (Min)
• Port C: Output (Hr)
• In mode 0

- Two 8-bit ports and two 4-bit ports

- Any port can be input or output

- Outputs are latched, inputs are not latched

​

I/O port Addressing-8255

8255

CS^b

​

A1

A0

​

RD^b

WR^b

A7

A6

A5

A4

A3

A2

A1

A0

​

IOR^b

IOW^b

Reset

Reset

Port A=80H

Port C=82H

Port B=81H

8255: Mode 0, Example 1

• Configure
• Port A, B and C as out port
• Control word
• Address: 80H, 81H ,82H for ABC

​

​

​

80H

Interface Program

MVI A,80H ; Load acc with Control word

OUT 83H ; Load control register with 83 at port address 83

CALL BUSYWAIT()

ISRDISPLY:

CALL GETTIMESTOREAT2000()

MOV A, 2000H

OUT 81H ; Write to LEDs

MOV A, 2001H

OUT 82H ; Write to LED

MOV A, 2002H

OUT 83H ; Write to LED

RET

​

Thanks