51 single chip timer works

51 MCU timer working principle and usage

TMOD : Controls how the timer works. 8 bits, the upper four bits control T1, and the lower four bits control T0. Because the timer has 4 modes of operation; TMOD = 0x00 (working mode 0), TMOD = 0x01 (working mode 0), TMOD = 0x02 (working mode 2), TMOD = 0x03 (working mode 3). The above is to control the lower 4 bits, so it corresponds to T0.

TR0: T0 timer enable switch, TR0 = 1, start working; =0 stop working.

ET0: T0 timer interrupt switch, when the timing time is up, it will run to interrupt the program. ET0=1, interrupt enable, 0 disable.

EA: Interrupt the main switch, you can imagine the total switch of the circuit, EA = 1, interrupt enable; =0, interrupt disabled.

TH0, TL0: T0 timer count register, which constitutes 16-bit count, 0x0000--0xFFFF (0--65535), as long as TH0TL0=0xFFFF (65535), the program will run to interrupt the program. In the interrupt program, we want Re-assign TH0, TL0.

If we say that we are timing 50 milliseconds, what value does TH0 and TL0 correspond to? As we said above, TH0, TL0, the 16-bit counter count range is 0---65535. 50ms = 50 000us, we only need to let TH0 TL0 count from (65535 - 50000), TH0, TL0 will continue to +1, until TH0, TL0 = 65535, is counted 50,000 times, the time is over 50ms. We only need to reassign to TH0 in the interrupt program, TL0 = (65535 - 50000), the timer will be interrupted every 50ms.

Therefore, TH0=(65535-50000)/256; TL0 = (65535-50000)%256;

Ok, T0 program example, timing 20ms program:

TO 20ms example program

After finishing the TO, what should I do with T1? I said at the beginning, TO, T1 is a pair of twins. Everyone puts the above T0 example program:

(TMOD = 0x01, ET0, TR0, TH0, TL0, interrput 1)

(TMOD = 0x10, ET1, TR1, TH1, TL1, interrput 3) This becomes the T1, timer program.