When we are learning a single-chip machine, our first routine is the flashing of the lamp. It is done with the delay program. Now I think so, don't be very appropriate, why? Our main program has a flashing of the lamp, you can't do anything else, can the single-chip microcontroller can only work? Of course, we can use the timer to implement the flashing function of the lamp.
Example 1: Query method
ORG 0000H
AJMP START
ORG 30H
Start:
MOV P1, # 0ffh;
MOV TMOD, # 00000001B; Timed / Counter 0 works in mode 1
Mov TH0, # 15h
MOV TL0, # 0a0h; ie 5536
Setb TR0; Timed / Counter 0 starts running
LOOP: JBC TF0, Next; If TF0 is equal to 1, then clear TF0 and turn NEXT
Ajmp loop; otherwise running to LOOP
Next: CPL P1.0
Mov TH0, # 15h
MOV TL0, # 9FH; Reset Timer / Counter
Ajmp loop
End ajmp loop
End
Type the program, what did you see? The lamp is flashing, which is done with timer, no longer the loop of the main program. Simply analyze the program, why use JBC? TF0 is the overflow marker of timing / counter 0, and when the timer generates overflow, the bit is changed by 0, so queries whether the bit can be known when it is. After this bit is 1, you need to use the software to clear the marking bit, so that the next timing is between 0 changing 1, so it uses JBC instructions, which is the judgment 1 transfer, and will Clear 0.
The above program is able to achieve the flashing, but the main program can't make anything else, or do it! No, no, we can insert some instructions between loops: ... and the AJMP LOOP instructions, as long as the time to perform these instructions is less than the timing. Then we can use some instructions to replace DJNZ when using software delay programs? Yes, but then ask you to accurately calculate the time of the instruction used, then subtract the corresponding number of corresponding DJNZ cycles, it is very inconvenient, and now only requires the instructions used less than the timing, obviously low. Of course, this method is still not good, so we often use the following methods to achieve.
Program 2: Implementation with interrupt
ORG 0000h,
AJMP START
ORG 000BH; Interrupt vector address of Timer 0
AJMP Time0; Jump to the real timer program
ORG 30H
Start:
MOV P1, # 0ffh;
MOV TMOD, # 00000001B; Timed / Counter 0 works in mode 1
Mov TH0, # 15h
MOV TL0, # 0a0h; ie 5536
Setb EA; open total interrupt allowed
Setb ET0; Opening Time / Counter 0 Allow
Setb TR0; Timed / Counter 0 starts running
LOOP: AJMP loop; Really, you can write any program here
Time0:; Interrupt handler for timer 0
PUSH ACC
Push PSW; push PSW and ACC into stack protection
CPL P1.0
Mov TH0, # 15h
MOV TL0, # 0a0h; reset timing constant
POP PSW
POP ACC
Reti
End
In the above routine, the timing time is between, the TF0 is changed from 0, which will cause the interrupt, the CPU will automatically turn to 000B to find the program and execute, because there is only 8 bytes of space to the timer interrupt, obviously insufficient To write all the interrupt handles, a jump instruction is arranged at 000B, and go to the actual processing interrupt, so that the interrupt program can be written in any place, and can write any length. After entering the timed interrupt, first save the current state, only the programs are demonstrated to save ACC and PSW, and the values that may be changed can be pushed into the stack as needed in the actual operation (this is not actually You need to save any value, here only make a presentation).
After the two microcontroller programs above, we found that the lights flicker were very fast, and they couldn't find out, but they only visually felt a little shake, why? We can calculate the number of preset in the timer is 5536, so 60,000 pulses per meter is time time, how much is this 60,000 pulse? Our crystal oscillator is 12m, so it is 60000 microseconds, that is, 60 milliseconds, so the speed is very fast. What should I do if I want to implement a 1S timing? At the end of this crystal oscillator, the longest timing is 65.536 milliseconds! A routine is given above.
ORG 0000H
AJMP START
ORG 000BH; Interrupt vector address of Timer 0
AJMP Time0; Jump to the real timer program
ORG 30H
Start:
MOV P1, # 0ffh;
MOV 30H, # 00H; Software Counter Pred Eqing 0
MOV TMOD, # 00000001B; Timed / Counter 0 works in mode 1
Mov TH0, # 3ch
MOV TL0, # 0b0h; ie 15536
Setb EA; open total interrupt allowed
Setb ET0; Opening Time / Counter 0 Allow
Setb TR0; Timed / Counter 0 starts running
LOOP: AJMP loop; Really, you can write any program here
Time0:; Interrupt handler for timer 0
PUSH ACC
Push PSW; push PSW and ACC into stack protection
INC 30H
Mov a, 30h
CJNE A, # 20, T_RET; Is the value of the 30H unit to 20?
T_L1: CPL P1.0; arrived, reflect P10
MOV 30H, # 0; Qing Software Counter
T_ret:
Mov TH0, # 15h
MOV TL0, # 9fh; reset timing constant
POP PSW
POP ACC
Reti
End
First analyze your own, see how it is achieved? Here, the concept of the software counter is used. The idea is such that the timer / counter 0 is used to do a 50 millisecond timer, and the timing is not immediately reflecting the P10 immediately, but adds the value in the software counter 1, If the software counter is 20, take the reverse P10 and clear the value in the software counter, otherwise it will be returned directly, so that it has become 20 timing interrupts to take anti-one P10, so the timing is extended to 20 * 50 is 1000 milliseconds. Read more
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