Which of the following statements are correct for a microcontroller ? A. A microcontroller has on-chip I/O ports B. A microcontroller has a fixed amount of RAM on the chip C. The flag register in the 8051 is called program standard word D. Auxiliary carry flag is set when there is a carry from D3 to D4 during an ADD or SUB operation E. Overflow flag is only used to detect errors in unsigned arithmetic operations. Choose the correct answer from the options given below :
A, B, D only
What defines a microcontroller. Unlike a microprocessor, which is only a CPU needing external memory and I/O chips, a microcontroller is a complete computer on one chip: CPU + ROM + RAM + I/O ports + timers + serial port + interrupt logic. Judge the statements against that, taking the 8051 as the reference device.
A — "A microcontroller has on-chip I/O ports." TRUE. The 8051 provides four 8-bit bidirectional ports (P0–P3), so LEDs, switches, LCDs and sensors can be wired directly with no external peripheral IC.
B — "A microcontroller has a fixed amount of RAM on the chip." TRUE. The on-chip memory is fixed at manufacture — 128 bytes of internal RAM and 4 KB of ROM in the classic 8051. This is a defining limitation: you cannot enlarge the internal RAM, only add external memory (up to 64 KB) if the device permits it.
C — "The flag register in the 8051 is called program standard word." FALSE. It is the PSW — Program Status Word — holding CY, AC, F0, RS1, RS0, OV and P.
D — "AC is set when there is a carry from D3 to D4." TRUE. The auxiliary carry flags a carry across the nibble boundary, and the DA A instruction uses it (together with CY) to correct the result of BCD addition.
E — "Overflow flag is only used to detect errors in unsigned arithmetic." FALSE. OV is the signed-arithmetic error flag: it is set when the result of a two's-complement operation falls outside the −128 to +127 range, i.e. when the carry into bit 7 differs from the carry out of bit 7. Unsigned overflow is reported by CY, not OV.
The true statements are A, B and D.
Quick illustration of the OV/CY distinction. Adding 7FH + 01H = 80H sets OV (as a signed sum, +127 + 1 wrongly gives −128) but leaves CY = 0; adding FFH + 01H = 00H sets CY (unsigned overflow) but leaves OV = 0.
Hence, the correct answer is A, B and D only.
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
