51 MCU Tutorial from Scratch - MCU Timer/Counter Experiment

We have done the timer experiment before, now let’s take a look at the counting experiment.

There are often two requirements for counting at work: first, to display the counted value, and second, to interrupt and alarm when the counted value reaches a certain level. The first type is various counters and odometers, and the second type is the counting on the production line mentioned in the previous example. Let's look at the first type first. Our hardware is connected like this: the oscillator composed of 324 is connected to the external pin T1 of the timer/counter 1. We use this to do a counting experiment. To display the counted value, of course, it is best to use a digital tube, but we haven't talked about this part yet. In order to avoid complicating the problem, we use the 8 LEDs of the P1 port to display the counted data.

The procedure is as follows:

ORG 0000H ,http://www.51hei.com

AJMP START

ORG 30H

START:

MOV SP,#5FH

MOV TMOD,#01000000B; Timer/Counter 1 is used for counting, no need to set all 0s

SETB TR1 ;Start counter 1 to start running.

LOOP: MOV A,TL0

MOV P1,A

AJMP LOOP

END

Connect the output of 324 to T1 with a wire (there are pads on the printed board) and run this program. Pay attention to placing the board in the correct position (LM324 is placed on the left hand side, and the LEDs are arranged from high to low). What do you see? As the LED connected to 324 flashes, the 8 LEDs of the microcontroller are also changing continuously. Pay attention to observe whether they are in binary:

00000000

00000001

00000010

00000011

Is the order changing? That's right, this is the data in TL0.

Procedure 2:

ORG 0000H

AJMP START

ORG 001BH

AJMP TIMER1 ; Timer 1 interrupt processing

ORG 30H

START: MOV SP,#5FH

MOV TMOD,#01010000B; Timer/Counter 1 is used for counting, mode 1, 0 is not used, all bits are set to 0

MOV TH1,#0FFH

MOV TL1,#0FAH; preset value, requiring every 6 pulses counted to be an event

SETB OF

SETB ET1; Enable general interrupt and timer 1 interrupt

SETB TR1 ;Start counter 1 to start running.

AJMP $

HOUR1:

PUSH ACC

PUSH PSW

CPL P1.0; when the count value reaches, P1.0 is inverted

MOV TH1,#0FFH

MOV TL1,#0FAH ; Reset the initial value of the count

POP PSW

POP ACC

RARELY

END

The work done by the above single-chip program is very simple, that is, to invert P1.0 once after every 6 pulses arrive, so the result of the experiment should be: the LED connected to the LM324 turns on and off 6 times, and the LED connected to the P1.0 port turns on or off once. This is actually the second application of the counter we mentioned above.

Procedure 3: External interrupt experiment

ORG 0000H

AJMP START

ORG 0003H ;Direct entry to external interrupt

AJMP INT0

ORG 30H

START: MOV SP,#5FH

MOV P1,#0FFH; all lights off

MOV P3,#0FFH; Set P3 port to high level

SETB OF

SETB EX0

AJMP $

INT0:

PUSH ACC

PUSH PSW

CPL P1.0

POP PSW

POP ACC

RARELY

END

The function of this program is very simple. Pressing button 1 (connected to pin 12) once will trigger interrupt 0 and invert P1.0. Therefore, theoretically, pressing it once will turn the light on and pressing it once will turn the light off. However, in actual experiments, you may find that sometimes it does not work. When you press it, it does not respond, but most of the time it is correct. What is going on? We will explain this when we talk about the keyboard. There is no problem with this program itself.