f the crystal frequency is 4.5 MHz, determine the time for setting the timer flag for mode 1 if TH0 starts at 00H.1 point12 ms2 ms174.78 ms50 ms

1. Break Down the Problem

We need to calculate the time it takes to set the timer flag for mode 1 of a timer using a crystal frequency of 4.5 MHz, starting with TH0 at 00H.

2. Relevant Concepts

In timer mode 1:

• The timer counts from TH0 and TL0 until it overflows.
• The timer frequency can be calculated based on the crystal frequency.
• The timer overflow occurs when the timer value reaches 0xFFFF (65535 in decimal).

3. Analysis and Detail

• Step 3.1: Calculate the Timer Frequency

  • The formula to calculate the timer frequency from the crystal frequency is: $\text{Timer Frequency} = \frac{\text{Crystal Frequency}}{12}$
  • For a crystal frequency of 4.5 MHz: $\text{Timer Frequency} = \frac{4.5 \, \text{MHz}}{12} = 0.375 \, \text{MHz} = 375 \, \text{kHz}$

• Step 3.2: Calculate the Timer Period

  • The timer period (time for one tick of the timer) is the reciprocal of the timer frequency: $\text{Timer Period} = \frac{1}{\text{Timer Frequency}} = \frac{1}{375 \times 10^3} \approx 2.67 \, \mu s$

• Step 3.3: Calculate the Overflow Time for Mode 1

  • The number of counts before overflow is $65536$ (from 0x0000 to 0xFFFF).
  • The total time to overflow is: $\text{Total Time} = \text{Number of Counts} \times \text{Timer Period} = 65536 \times 2.67 \times 10^{-6} \approx 0.175 \, \text{s} = 175.76 \, \text{ms}$

4. Verify and Summarize

In sum, the time taken to set the timer flag in mode 1, starting from TH0 at 00H, is approximately 175.76 milliseconds.

Final Answer

The time for setting the timer flag for mode 1, starting at TH0 = 00H, is approximately 175.76 ms.