Question

Assuming A 4-MHz Crystal Is Used, What Value Of N Would Lead To 2.5 Milliseconds Delay?

LDX #N ; 2 cycles
DELAY: DEX ; 1 cycle
BNE DELAY ; 4 (back)/2(down) cycle(s)

Answer 1

The value of N that would lead to a 2.5 millisecond delay is 10,000.

Step-by-step explanation:

To calculate the delay, we need to determine the number of cycles that will occur in 2.5 milliseconds. Since the frequency of the crystal is given as 4 MHz (4 million cycles per second), we can calculate the number of cycles within 2.5 milliseconds using the formula:

Number of cycles = Frequency × Time

Substituting the given values:

Number of cycles = 4 MHz × 2.5 ms = 4,000,000 cycles/s × 0.0025 s = 10,000 cycles

Therefore, the value of N that would lead to a 2.5 millisecond delay is N = 10,000.

Answer 2

The value of N needed for a 2.5 milliseconds delay using a 4-MHz crystal with the given instruction cycle times is approximately 1429.

Step-by-step explanation:

The student is asking about determining the value of N required to create a specific delay in milliseconds when using a 4-MHz crystal with an assembly language loop for a microcontroller or processor. This involves understanding the instruction cycle times and calculating the number of loop iterations needed to achieve the delay.

Steps to Calculate the Value of N

Firstly, we need to calculate the time taken for one iteration of the loop:

LDX #N; takes 2 cycles

DEX; takes 1 cycle

BNE DELAY; takes 4 cycles when branching, and 2 cycles when falling through (not taken).

The loop runs until the zero condition is met. Assuming the BNE instruction always branches, each iteration takes 2 + 1 + 4 = 7 cycles. Given the 4-MHz crystal, the cycle time is 1/(4*10^6) seconds per cycle. Thus, the desired 2.5 milliseconds delay corresponds to 2.5*10^-3 seconds.

To find N, we use the formula N = (Desired time delay) / (Cycle time * Loop iteration time). Substituting the values, we get:

N = (2.5*10^-3) / (1/(4*10^6) * 7) approximately equals (2.5*10^-3) * (4*10^6) / 7.

Therefore, N is roughly equal to 1,428.57, and since N must be an integer, we round it to 1429.