Basics and Applications of Microcontrollers

1. Clock Timing

(1) Clock Timing Setup

Using the timer/counter of the 80C51 to achieve clock timing is a great application topic. The explanation is as follows:

• Calculate the initial count value.

• Use interrupt mode, that is, accumulate the number of timer overflows through the interrupt service routine, and when it reaches 8 times, it indicates one second timing.

• Implement timing from seconds to minutes and from minutes to hours through value accumulation and comparison in the program.

• Set up a clock display buffer.

(2) Program Flow

① Main Program MAIN

② Interrupt Service Routine PIT0

③ Increment Subroutine DAAD1

The increment operation includes the following three items:

• Merging numbers. Since each LED display corresponds to an 8-bit buffer unit, the time value represented by two BCD codes occupies one buffer unit each and only occupies its low 4 bits. Therefore, before the increment operation, the values stored in the two buffer units need to be merged to form one byte, and then the increment operation can be performed. This is also called “merging bytes”.

• Decimal adjustment. After incrementing, decimal adjustment is required.

• Fraction. The incremented time value is split back into two bytes and sent back to their respective buffer units.

2. Digital Thermistor Thermometer

(1) Thermistor Temperature Conversion Principle

Where:

• t is the measured temperature

• t₀ is a temperature parameter related to the thermistor characteristics.

• K is a coefficient related to the thermistor characteristics.

• V_T is the voltage across the thermistor.

(2) Basic Circuit

Assuming the use of ADC0809 for A/D conversion. The circuit connection is shown in the figure below

Digital Thermistor Thermometer

(3) Program Design

1) Temperature Calculation Program

COMP: MOVB, #0XXH ; Send the expanded K value of 256 to B

MULAB; 256×K×VT

MOVA, #0YYH ; Send T0 value to A, discard the low 8 bits of the product

CLRC ; Clear carry bit

SUBBA, B; t0-K×VT

CJNEA, #0AH, COMP1

COMP1: JNC COMP4 ; If temperature is below 10℃, display F

CJNEA, #97H, COMP2

COMP2: JC COMP3 ; If temperature is below 151℃, then branch

COMP4: MOV 27H, #0FH ; Exceeding effective temperature range, display F

MOV28H, #0FH

MOV29H, #0FH

MOV2AH, #0FH

MOV2BH, #0FH

MOV2CH, #0FH

ACALLDISP ; Call display subroutine

COMP3: RET

2) Temperature Value Conversion to Decimal Program

MOVR1, #00H

MOVR2, #00H

CLRC

CHAN: SUBBA, #64H ; Subtract 100

JCCHAN1 ; If not enough to subtract, then branch

INCR1 ; Enough to subtract, effective position 1

AJMPCHAN2

CHAN1: ADDA, #64H; Restore coefficient

CHAN2: SUBBA, #0AH ; Subtract 10

JCCHAN3 ; If not enough to subtract, then branch

INCR2 ; Enough to subtract, increment the tens digit by 1

AJMPCHAN2; Repeat subtracting 10

CHAN3: ADDA, #0AH; Restore the unit digit

MOV27H, #0AH

MOV28H, #0DH

MOV29H, #10H

MOV2AH, R1

MOV2BH, R2

MOV2CH, A

RET