In 8051 microcontroller, one machine cycle lasts in 12 oscillation period. Crystal oscillator's frequency is 11.0592 MHz. Find how long it takes to execute instruction MOV R4, # 25.
1.085 µs
The timing rule for the 8051. Instruction times are quoted in machine cycles, and in the standard 8051 one machine cycle occupies 12 oscillator periods (it comprises six states S1–S6, each of two oscillator phases).
Step 1 — find the machine-cycle time from the crystal frequency.
\(T_{mc} = \dfrac{12}{f_{osc}}\)
Step 2 — substitute fosc = 11.0592 MHz.
\(T_{mc} = \dfrac{12}{11.0592\times10^{6}} = 1.085\times10^{-6}\ \text{s} = 1.085\ \mu s\)
Equivalently, the machine-cycle frequency is \(11.0592\ \text{MHz}/12 = 921.6\ \text{kHz}\), whose period is 1.085 µs.
Step 3 — how many machine cycles does the instruction take? MOV R4, #25 loads an immediate constant into a register-bank register. It is a 2-byte instruction that executes in one machine cycle, so:
\(t = 1 \times 1.085\ \mu s = 1.085\ \mu s\)
Why 11.0592 MHz is the classic 8051 crystal. Dividing it by 12 and then by 32 gives exactly 28800, so the serial port can generate standard baud rates (9600, 19200, …) with zero error — which is why almost every 8051 timing question uses this value and the resulting 1.085 µs machine cycle.
Useful reference points. Most 8051 instructions take 1 or 2 machine cycles; MUL AB and DIV AB take 4. So a 2-cycle instruction here would take 2.17 µs, and MUL AB would take 4.34 µs.
Hence, the instruction MOV R4, #25 takes 1.085 µs to execute.
Similar Questions
Given below are two statements :
Statement I : In 8051 micro-controller register banks and stack reserves 32 bytes from locations 00 to 1F Hex
Statement II : Bit-Addressable RAM locations are 20 H to 2 F H.
In the light of the above statements, choose the most appropriate answer from the options given below :
Find the delay generated by Timer 0 in the following code of 8051 microcontroller : clock period = 1.085 µs.
MOV TMOD, #01H
MOV TLO, #3DH
MOV THO, #0A2H.
SET B TRO
Loop : J N B TFO, LOOP
CLR TRO
CLR TFO
In "JZ Next" instruction of 8051 microcontroller, which register's content is checked to see if it is zero?
Using 8051 assembly language programming numbers 54 H and 98 H are added. After addition the status of CY, AC and P flags are respectively:
Advantage of segmented memory in 8086 is
A. Allows the memory capacity to be 1M byte, although the actual address is of 16 bit size.
B. Allows the placing of code and data portions of the same program in different parts of memory.
C. Allows the memory capacity to be 2M byte, although the actual address is of 16 bit size.
D. Allows the placing of code and data portion of the same program in same parts of memory.
E. Allows the memory capacity to be 1M byte, although the actual address is of 20 bit size
Choose the correct answer from the options given below :
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 :
Match List I with List II
LIST I (instruction of 8051 microcontroller) LIST II (Addressing mode) A. MOV A, # 32 H I. Register addressing mode B. MOV R 6, A II. Register Indirect addressing mode C. MOV R4, 7 FH III. Immediate Addressing mode D. MOV A, @ RO IV. Direct Addresing mode Choose the correct answer from the options given below:
The ALE line of an 8085 microprocessor is used to
Contents of ‘A’ register after execution of the following 8085 microprocessor program is
MVI A, 55 h
MVI C, 25 h
ADD C
DAA
Word 20 contains 40
Word 30 contains 50
Word 40 contains 60
Word 50 contains 70
Which of the following instructions loads 60 into the accumulator ?
(a) load immediate 60
(b) load direct 30
(c) load indirect 20
(d) load indirect 30
Which of the above statements are correct ?
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Register which is used to store values of arithmetic and logical operations is termed:
How many bytes of bit addressable memory is present in 8051 based microcontrollers?
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