After the timer is initialized, its value cannot be changed?-EEWORLD

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Yesterday a classmate asked me how to implement a function of a microcontroller:

1:
If you press KEY1, the 30S countdown will start.
If you press KEY2, the function will be executed and the 30S countdown will be canceled.
2:
If you press KEY1, the 30S countdown will start
. If you press KEY2, the function will be executed and the 30S countdown will be canceled.

After inquiry, it belongs to requirement 1 and uses a matrix keyboard.

Interestingly, I thought requirement 2 was easier to achieve, and I did it right away, but I thought about requirement 1 for a long time. The problem was that after pressing KEY2 to execute other programs, pressing KEY1 did not restart the countdown. I always wondered if I could reassign the timer value, and tried to modify various related registers. It was very strange that after initialization, the timer value seemed to be unable to be changed? I searched online, but could not find any relevant questions.

But in a flash, the answer flashed through my mind, and the final program is as follows (most of the programs and variable definitions are omitted):

void main()

{

init(); // Initialization of timing interrupt

while(1)

{

keyscan();

if (1 == keynum)

{

disp(); //Nixie tube displays countdown

LED = 1;

keyscan();

}

if (2 == keynum)

{

LED = 0;

keyscan();

time = 30; //This is the sentence that implements the countdown again

}

void tim1(void) interrupt 1

{

TH0 = (65535-62484)/256;

TL0 = (65535-62484)%6;

timer++; //Because the timer cannot achieve one-second timing, use a variable to achieve

if (timer >= 16)

{

timer = 0;

time--;

if( time <= 0)

time = 30; // used for time display

}

The solution to the problem is to reassign the displayed number to 30. Don't worry about the current status of the timer, because the effect is for people to see. As long as the observed appearance meets the requirements, it's fine. Programming is often like this. Although it is not clear whether it affects the accuracy of timing, this way of thinking about the problem from a different angle is indeed a sharp idea.

Keywords：Timer Reference address：After the timer is initialized, its value cannot be changed?

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