Contents of ‘A’ register after execution of the following 8085 microprocessor program is MVI A, 55 h MVI C, 25 h ADD C DAA
80 h
Execute the program one instruction at a time.
\(\texttt{MVI A, 55H}\) — loads the immediate value 55H into the accumulator.
\(\texttt{MVI C, 25H}\) — loads 25H into register C.
\(\texttt{ADD C}\) — adds C to A in plain binary:
\(55H+25H=7AH\)
(Nibble by nibble: 5 + 5 = A, and 5 + 2 = 7.) Note that 7AH is not valid packed BCD, because the digit A is outside 0–9 — which is precisely why the next instruction exists.
\(\texttt{DAA}\) — Decimal Adjust Accumulator. Its two rules are:
1. If the lower nibble exceeds 9, or the auxiliary carry AC is set, add 06H.
2. If the upper nibble then exceeds 9, or the carry CY is set, add 60H.
Here the lower nibble is A = 10, which is greater than 9, so rule 1 applies:
\(7AH+06H=80H\)
The upper nibble is now 8, which is 9 or less, and CY is clear, so rule 2 does not fire.
\(A = 80H\)
Check it in decimal. Read the operands as BCD: 55 + 25 = 80, and the accumulator indeed holds 80 in packed BCD ✓. The correction works because binary carries at 16 while decimal carries at 10, so adding 6 makes up the difference whenever a nibble overflows past 9.
Why the distractors appear. 7AH is the value before DAA — the trap for anyone who stops after the ADD. 50H and 22H correspond to mis-applying the correction or adding the digits as raw hexadecimal.
One caution about DAA. It works only immediately after an addition and only on the accumulator; the 8085 has no equivalent instruction for subtraction, so BCD subtraction is done by adding the ten's complement.
Hence, after DAA the accumulator contains 80H.
Similar Questions
In an 8086, AL = 19 BCD & BL = 36 BCD prior to execution of following example
ADD AL, BL
DAA
What will be content of AL after execution of the example ?
If SS = 3000 H and SP = 2000 H in 8086 microprocessor, in which memory addresses the contents of BL and BH are stored respectively, when PUSH BX instruction is executed.
The BIU of 8086 contains 16 bit segment registers. What is the width of address sent out by BIU of 8086 miocroprocessor?
Loop 1 : MOV A, P1
MOV P2, A
JNB P3.3, Loop1
The program does the following
In 8051 micro controller
A. INT0 and INT1 pins are normally low
B. Timer1 Interrupt Flag is auto cleared after occurrence
C. Serial interrupt is auto cleared after occurrence
D. Timer 0 Vector location is 000B H
Choose the correct answer from the options given below:
In 8086
A. The stack memory is a FIFO (First In First Out)
B. The JMP instruction cannot be prefixed with segment override prefix
C. SAHF and POPF instructions affect the flag register
D. DAS instruction cannot be used for 8 bit operations.
Choose the correct answer from the options given below :
In 8051
A. INT0 and INT1 can be made edge triggered by programming TCON
B. On reset serial communication interrupts has highest priority
C. Upon reset all interrupts are enabled
D. Only one interrupt is set aside for serial communication.
Choose the correct answer from the options given below:
Match List I with List II in 8086 Micro processor
LIST I LIST II A. Direct memory addressing data memory I. MOV [SI], 2500 H B. Immediate Addressing II. PUSHF C. Flag Manipulation III. RET D. Control transfer IV. MOV BX, [2000 H] Choose the correct answer from the options given below:
Arrange following interrupts in order of polling (checking interrupt conditions) after every instructions.
A. Serial Interrupt
B. External 1 Interrupt
C. Timer 1 Interrupt
D. External 0 Interrupt
Choose the correct answer from the options given below :
Given below are two statements : one is labelled as Assertion A and the other is labelled as Reason R
Assertion A : Some instruction read the contents of an internal port latch instead of reading the status of an external pin.
Reason R : We must not make a distinction between reading the status of the input pin and internal latch of the output port.
In the light of the above statements, choose the most appropriate answer from the options given below :
Important Questions from Microprocessors
An 8086 address bus is a/an _____ -bit bus
Program counter for any counter:
In the pin out configuration of the 8085 microprocessor, the sequential input data is represented by
Which of the following functions is not performed by a microprocessor?
Match the columns.
Pin
Description
a. D 0-D 7
1. Reset Input
b. RESET
2. Data Lines
c. A 0,A 1
3. Internal Address
