Timing Counter T0 Timing Application Technology (Part 2)

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Timing Counter T0 Timing Application Technology (Part 2) [Copy link]

1. Experimental tasks

The AT89S51 timer/counter T0 generates a 2-second timer. When the 2-second timer comes, the indicator light flashes. The frequency of each indicator flashing is 0.2 seconds. That is to say, the L1 indicator light flashes at a rate of 0.2 seconds at the beginning. When the 2-second timer comes, L2 starts to flash at a rate of 0.2 seconds, and so on. The flashing rate of 0.2 seconds is also completed by the timer/counter T0.

2. Circuit diagram

3. System board hardware connection

(1) The hardware settings are the same as in many previous tests. Please set them yourself
. (2) Pay attention to whether the I/O ports in the program are consistent with the hardware settings.

4. Program design content
(1. Since the interrupt method is used, the interrupt source must have its interrupt entry address. For timer/counter T0, the interrupt entry address is 000BH, so a long jump instruction is added at the interrupt entry to execute the interrupt service program. The format of writing the assembly source program is as follows:
ORG 00H
LJMP START
ORG 0BH; Timer/counter T0 interrupt entry address
LJMP INT_T0
START: NOP; Main program starts
.
.

INT_T0: PUSH ACC; Timer/counter T0 interrupt service program
PUSH PSW
.
.
POP PSW
POP ACC
RETI; Interrupt service program returns
END
(2. Timing for 2 seconds, using 16-bit timing for 50ms, a total of 40 times of timing can reach 2 seconds, an interrupt is generated every 50ms, and the 40 times of timing are completed in the interrupt service program. Similarly, 0.2 seconds of timing requires 4 times to reach 0.2 seconds. For the interrupt program, the interrupt must be disconnected in the main program.
(3. Since each 2-second timer expires, L1-L4 flash alternately. Use ID to identify. When ID = 0, L1 flashes; when ID = 1, L2 flashes; when ID = 2, L3 flashes; when ID = 3, L4 flashes

5. Assembly source program
TCOUNT2S EQU 30H
TCNT02S EQU 31H
ID EQU 32H
ORG 00H
LJMP START
ORG 0BH
LJMP INT_T0
START: MOV TCOUNT2S,#00H
MOV TCNT02S,#00H
MOV ID,#00H
MOV TMOD,#01H
MOV TH0,#(65536-50000) / 256
MOV TL0,#(65536-50000) MOD 256
SETB TR0
SETB ET0
SETB EA
SJMP $
INT_T0: MOV TH0,#(65536-50000) / 256
MOV TL0,#(65536-50000) MOD 256
INC TCOUNT2S
MOV A,TCOUNT2S
CJNE A,#40,NEXT
MOV TCOUNT2S,#00H
INC ID
MOV A,ID
CJNE A,#04H,NEXT
MOV ID,#00H
NEXT: INC TCNT02S
MOV A,TCNT02S
CJNE A,#4,DONE
MOV TCNT02S,#00H
MOV A,ID
CJNE A,#00H,SID1
CPL P1.0
SJMP DONE
SID1: CJNE A,#01H,SID2
CPL P1.1
SJMP DONE
SID2: CJNE A,#02H,SID3
CPL P1.2
SJMP DONE
SID3: CJNE A,#03H,SID4
CPL P1.3
SID4: SJMP DONE
DONE: RETI
END