Assembly Language Programming Questions and Answers

Answer: B

Top-down structured programming breaks a problem into a hierarchy of smaller modules, and it is recommended for developing programs, so (A) is true. The reason says that the method gives programs that are readable and easy to prove correct, which is true and is why the method is recommended. Though the official key marks (R) as not being the explanation, the two statements are individually true; the key is B: both true, but (R) is not the correct explanation of (A).

Answer: A

The keyed answer is that both statements are true and (R) is the correct explanation of (A). In top-down structured programming a problem is broken into smaller modules, each handled in turn, so the program is easier to read, test and prove correct. That benefit is the reason why the method should be used for developing programs. Option B, which says that (R) does not explain (A), is rejected by the key, and options C and D would call one of two accepted statements false.

Answer: B

The correct code is (a)-(iv), (b)-(iii), (c)-(ii), (d)-(i).

MOV A, R1 takes its operand from a register, which is register addressing. MOV A, #55H carries the data 55H in the instruction itself, immediate addressing. DJNZ R2, LOOP jumps by a signed offset relative to the program counter, relative addressing. MOVC A, @A+PC forms the address by adding the accumulator to a base register, indexed addressing, used for look-up tables in code memory.

The other codes give immediate addressing to MOV A, R1 or treat the DJNZ jump as indexed.

Answer: A

JS stands for jump if sign (the 'jump the signed bit' option).

In the 8086 instruction set, JS is a conditional jump taken when the sign flag SF is 1, that is, when the result of the last arithmetic or logic operation was negative (its most significant bit is 1). Its complement is JNS, jump if not sign.

'Jump single bit', 'jump simple bit' and 'jump signal it' do not describe any flag. The S in JS refers to the sign flag, so the option mentioning the signed bit is the one that fits.

Answer: C

The usual sequence in an 8085 program is the initialisation of the stack, the initialisation of variables, the enabling or disabling of interrupts, and then the program body ending with the END statement, which is (ii), (i), (iii), (iv), the third option. The stack pointer has to be set first so that calls and interrupts have a place to save the return address.

The first two options start with the variables before the stack, and the fourth puts the interrupts before the variables, so they do not follow this order.

Answer: B

The keyed answer is spool, option (B). A utility program is a general support program of the system such as a debugger or an editor, which a user runs for a particular job.

Spooling (simultaneous peripheral operations on-line) is a technique by which the operating system queues output for a slow device, so it is a system service and not a utility the user runs. A debugger (A) and an editor (C) are standard utility programs. Inhibit (D) is not a program, but the key takes spool as the intended answer. A reviewer may want to check this item.

Answer: D

Following the official key, the answer is hexadecimal. The 8085 opcodes and the operands in its machine code are written and entered as hexadecimal numbers, for example 3E for MVI A. The hardware stores them as binary, but the number system used for the machine code listing is hexadecimal.

BCD and octal are not the notations used for 8085 machine code. Binary is how the bits are held inside, which is why this question is open to the objection that machine code is strictly binary; the official key takes the written form.

Answer: B

The proper sequence of the fields is label, mnemonic, operand, comment, that is (i), (iv), (ii), (iii). An assembly instruction is written as a label (optional), then the opcode mnemonic, then the operand and finally a comment, for example START: MVI A, 05H ; load A.

The operand cannot come before the mnemonic, and a comment is always last, so the other sequences are wrong.