Final answer:
With a crystal frequency of 4.5 MHz and TH0 starting at 00h, it takes approximately 14.55 milliseconds for the timer flag to be set in Mode 1 of a microcontroller timer.
Step-by-step explanation:
If the crystal frequency is 4.5 MHz, the time period of one cycle is the inverse of the frequency. To calculate this, we can use the formula:
Time period (T) = 1/frequency (f)
Substituting the given frequency:
T = 1/4,500,000 Hz = 0.222 × 10-6 seconds or 222 nanoseconds
For a timer in Mode 1, which typically operates on a 16-bit timer in a microcontroller, the count will start from the value in the TH0 register. If TH0 is set at 00h, it begins from 0. The timer will count up to its maximum value of 65,536 (since 16-bit max value is 216 - 1), at which point the timer flag is set, indicating an overflow.
Now, to find out the time for the timer to set the flag:
Total time = Timer cycle time × Max count value
Total time = 222 ns × 65,536
Total time = 14,553,472 ns or approximately 14.55 milliseconds
Therefore, with a crystal frequency of 4.5 MHz, starting from 00h, it will take approximately 14.55 milliseconds for the timer flag to be set in Mode 1.