Answer the Following Questions: Question No. (1) (5 marks)

Answer the Following Questions:

Question No. (1) (5 marks)

1.1 Which type of JMP is used when jumping to any location within the current code segment?

Ans. A near JMP instruction

1.2 Which JMP instruction is 5 bytes long?

Ans. A far jump

1.3 Which type of JMP instruction (short, near) assembles for the following:

(a) if the distance is 0210H bytes

(b) if the distance is 0020H bytes

Ans. (a) near (b) short

1.4 The near jump modifies the program address by changing which register or registers?

Ans. The IP register

1.5 Explain what the JMP AX instruction accomplishes. Also identify it as a near or a far jump instruction.

Ans. The JMP AX instruction jumps to the offset address stored in AX. This can only be a near jump.

1.6 Describe how the JA instruction operates.

Ans. JA tests the condition of an arithmetic or logic instruction to determine if the outcome is above. If the outcome is above a jump occurs, otherwise no jump occurs.

1.7 Which conditional jump instructions follow the comparison of signed numbers?

Ans. JNE, JE, JG, JGE, JL, or JLE

1.8 Which conditional jump instructions test both the Z and C flag bits?

Ans. JA and JBE
1.9 Name the different flags control instructions, the operations performed by them and also the flags affected.
Ans. The following table shows the different flags control instructions, their meaning and the flags affected by respective instructions.

1.10 What are the two basic types of unconditional jumps? Explain.

Ans. The two basic types of unconditional jumps are intrasegment jump and intersegment jump.

The intrasegment jump is a jump for which the addresses must lie within the current code segment. It is achieved by only modifying the value of IP.

The intersegment jump is a jump from one code segment to another. For this jump to be effective, both CS and IP values are to be modified.

1.11 Distinguish between Short-label and Near-label jump instructions.

Ans. The distinction between the two is shown in a tabular form.



Question No. (2) (5 marks)

2.1 What are the two types of CALL instructions? Discuss.

Ans. The two types are: intrasegment CALL and intersegment CALL.

If the operands are Near-proc, Memptr16 and Regptr16, then they specify intrasegment CALL while Far-proc and Memptr32 represent intersegment CALL.

2.2 List the different LOOP instructions and also the operations they perform.
Ans. The different loop instructions and the operations they perform are shown in the following Table.

2.3 List the basic string instructions and the operations they perform.

Ans. The basic string instructions and the operations they perform are shown in following Table.

2.4 What is a ‘REP’ instruction? Discuss.

Ans. ‘REP’ stands for repeat and is used for repeating basic string operations—required for processing arrays of data.

There are a number of repeat instructions available and are used as a prefix in string instructions. The prefixes for use with the basic string instructions are shown in the following Table.

2.5 Which registers have their contents changed during an interasegment jump? Intersegment jump?
Ans. IP; CS and IP.

2.6 The following program implements a delay loop.

MOV CX,1000H

DLY: DEC CX

JNZ DLY

NXT: --- ---

(a) How many times does JNZ DLY instruction is executed?

(b) Change the program so that JNZ DLY is executed 17 times.

Ans.

(a) 100016 = 212 = 4096 times.

(b) Implement the loop with the counter = 17

MOV CX,11H

DLY: DEC CX

JNZ DLY

NXT: --- ---
2.7 What is the function is performed by RET instruction?

Ans. At the end of the subroutine a RET instruction is used to return control to the main (calling) program. It does this by popping IP from the stack in the case of an intrasegment call and both CS and IP for an intersegment call.

2.8 What determines the SI and DI registers show an increment or a decrement during string operation?

Ans. DF.

2.9 Which segment register is used to form the destination address for a string instruction?
Ans. ES.

2.10 Write equivalent instruction sequences using string instructions for each of the following:

(a)

MOV AL, [SI]

MOV AL, [DI]

INC SI

INC DI

(b)

MOV AX, [SI]

INC SI

INC DI

(c)

MOV [DI], AL

CMP AL, [SI]

DEC SI

DEC DI

Ans. The following two are the equivalent string instructions of the given ones:

(a)

CLD

MOV ES,DS

MOVSB

(b)

CLD

LODSW

(c)

STD

MOV ES,DS

CMPSB

Question No. (3) (10marks)

3.1 By what factor does the 8284A clock generator divide the crystal oscillator’s output frequency?

Ans. The factor is 3.

3.2 The PCLK output of the 8284A is ____________ MHz if the crystal oscillator is operating at 14 MHz.

Ans. 14 MHz/6 = 2.33 MHz

3.3 Which bus connections on the 8086 microprocessor are typically demultiplexed?

Ans. Address bus connection A₀–A₁₅

3.4 Why are buffers often required in an 8086/8088-based system?

Ans. If too many memory and/or I/O devices are attached to a system the buses must be buffered.

3.5 Contrast minimum and maximum mode 8086/8088 operation.

Ans. Minimum mode operation is most often used in embedded applications and maximum mode operation was most often used in early personal computers.

3.6 What is the purpose of the or pin on a memory component?

Ans. Select the memory device

3.7 The 2K EPROM shown in the following Figure is decoded at memory address locations FF800H–FFFFFH. Modify the NAND gate decoder of Figure 10–13 to select the memory for address range DF800H–DFFFFH.

Ans.

3.8 When the G1 input is high and both and are low, what happens to the outputs of the 74HCT138 3-to-8 line decoder?
Ans. One of the eight outputs becomes a logic zero as dictated by the address inputs.

3.9 The following Figure shows a circuit that uses eight 2764 EPROMs for a 64K 8 section of memory in an 8088 microprocessor-based system. The addresses selected in this circuit are F0000H–FFFFFH. Modify the circuit to address memory range 40000H–4FFFFH.

Ans.

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