Class 7 – Simple RPM Counter – BuddyKit

Hi buddies! In this post, let’s explore the Timer and Counter feature in the Buddy51 board.

Why use a Timer instead of NOP?

In our previous examples, we used NOP-based software delays. However, these are not accurate. To achieve precise timing, we use hardware-based timers and counters.

What is a Timer or Counter?

A timer or counter is a register that increments with each clock pulse. If the pulse is from an external pin, it’s a counter. If it’s from the system clock, it’s a timer. Once it overflows, a flag is set, which we use to take action.

Think of it like an alarm on your phone. When time is up, the alarm rings. Similarly, in the MCU, the flag is set when time is up.

Example: RPM Meter

An RPM meter counts the number of pulses from a proximity sensor in one second. Timer0 acts as the counter, and Timer1 is used for the 1-second delay.

Number of Timers

The Buddy51 has 3 timers:

Timer0
Timer1
Timer2

This can vary depending on the IC manufacturer.

Timer Modes in Buddy51

Buddy51 supports four timer modes: Mode 0, Mode 1, Mode 2, and Mode 3.

Mode 0: 13-bit timer, max count 8191. Rarely used.
Mode 1: 16-bit timer, max count 65536. Most commonly used.
Mode 2: 8-bit auto-reload mode. TL is counter, TH is reload value.
Mode 3: Split Timer Mode. Timer0 is split into two 8-bit timers. Timer1 is disabled in this mode.

Timer Initialization Steps

Select Timer and Mode
Load Timer Value
Start Timer
Check Overflow

Step 1: Timer and Mode Selection using TMOD

The TMOD (Timer Mode) register is an 8-bit register used to configure Timer0 and Timer1.

Bit	7	6	5	4	3	2	1	0
Label	GATE1	C/T1	M1	M0	GATE0	C/T0	M1	M0

GATE: Allows external signal to control timer
C/T: Selects between Counter (1) and Timer (0)
M1/M0: Select timer mode

Example: TMOD = 0x01; configures Timer0 in Mode 1.

Step 2: Load Timer Value

In 16-bit Mode, to generate 50ms delay with 11.0592MHz clock:

Machine cycle ≈ 1.085 microseconds
Counts needed = 50,000 / 1.085 ≈ 46080
Initial value = 65536 – 46080 = 19456 = 0x4C00

So, set:

THx = 0x4C;
TLx = 0x00;

1 2	THx = 0x4C; TLx = 0x00;

Step 3 & 4: Start Timer and Check Overflow

Use TCON (Timer Control Register):

Bit	7	6	5	4	3	2	1	0
Label	TF1	TR1	TF0	TR0	IE1	IT1	IE0	IT0

TR0: Start Timer0
TF0: Timer0 Overflow Flag

When TF0 is set, delay is complete.

Example: RPM Meter using Counter

Sensor input connected to P3.4 (T0 pin). Timer0 is Counter, Timer1 is 1s delay generator.

#include <8052.h>                  // Include 8051 microcontroller header
#include <stdio.h>                 // For sprintf function
#include "../library/LCD4/LCD4.h"  // BuddyKit LCD 4-bit mode library

// Function to create approximately 1-second delay using Timer 1
void Delay1Sec() {
    u8 ms50 = 20;                  // Loop 20 times for 20 * 50ms = ~1 second
    while (ms50--) {
        TH1 = 0x4C;                // Set Timer 1 high byte
        TL1 = 0x00;                // Set Timer 1 low byte
        TR1 = 1;                   // Start Timer 1
        while (!TF1);             // Wait until Timer 1 overflows
        TR1 = 0;                   // Stop Timer 1
        TF1 = 0;                   // Clear overflow flag
    }
}

void main() {
    u16 count = 0;                 // To store the number of pulses
    u8 buff[17];                   // Buffer to hold RPM display string
    u16 rpm = 0;                   // Variable to hold calculated RPM

    LCD_Init();                    // Initialize LCD
    LCD_Puts("HI BUDDIES!");       // Display welcome message on LCD

    TMOD = 0x15;                   // Timer 1 = Timer Mode, Timer 0 = Counter Mode
    P3_4 = 1;                      // INT0 pin (usually used with IR sensor input)

    while (1) {
        TH0 = 0x00;                // Reset Timer 0 high byte
        TL0 = 0x00;                // Reset Timer 0 low byte
        TR0 = 1;                   // Start Timer 0 (count pulses from IR sensor)

        Delay1Sec();               // Wait for 1 second

        TR0 = 0;                   // Stop Timer 0
        count = TL0 | (TH0 << 8);  // Combine high and low byte for final count
        rpm = count * 60;          // Convert to RPM (60 seconds)

        sprintf(buff, "RPM: %u", rpm);  // Format RPM to string
        LCD_ClearRow(2);                // Clear second row of LCD
        LCD_Puts(buff);                 // Display RPM value on LCD
    }
}

#include <8052.h> // Include 8051 microcontroller header

#include <stdio.h> // For sprintf function

#include "../library/LCD4/LCD4.h" // BuddyKit LCD 4-bit mode library

// Function to create approximately 1-second delay using Timer 1

void Delay1Sec() {

u8 ms50 = 20; // Loop 20 times for 20 * 50ms = ~1 second

while (ms50--) {

TH1 = 0x4C; // Set Timer 1 high byte

TL1 = 0x00; // Set Timer 1 low byte

TR1 = 1; // Start Timer 1

while (!TF1); // Wait until Timer 1 overflows

TR1 = 0; // Stop Timer 1

TF1 = 0; // Clear overflow flag

}

void main() {

u16 count = 0; // To store the number of pulses

u8 buff[17]; // Buffer to hold RPM display string

u16 rpm = 0; // Variable to hold calculated RPM

LCD_Init(); // Initialize LCD

LCD_Puts("HI BUDDIES!"); // Display welcome message on LCD

TMOD = 0x15; // Timer 1 = Timer Mode, Timer 0 = Counter Mode

P3_4 = 1; // INT0 pin (usually used with IR sensor input)

while (1) {

TH0 = 0x00; // Reset Timer 0 high byte

TL0 = 0x00; // Reset Timer 0 low byte

TR0 = 1; // Start Timer 0 (count pulses from IR sensor)

Delay1Sec(); // Wait for 1 second

TR0 = 0; // Stop Timer 0

count = TL0 | (TH0 << 8); // Combine high and low byte for final count

rpm = count * 60; // Convert to RPM (60 seconds)

sprintf(buff, "RPM: %u", rpm); // Format RPM to string

LCD_ClearRow(2); // Clear second row of LCD

LCD_Puts(buff); // Display RPM value on LCD

}

That’s it! Your basic RPM meter using Buddy51 is ready!

What’s Next?

In the next post, we’ll use timer + interrupt to build a real-time application.

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Class 7 - Simple RPM Counter

May 26, 2025

Why use a Timer instead of NOP?

What is a Timer or Counter?

Example: RPM Meter

Number of Timers

Timer Modes in Buddy51

Timer Initialization Steps

Step 1: Timer and Mode Selection using TMOD

Step 2: Load Timer Value

Step 3 & 4: Start Timer and Check Overflow

Example: RPM Meter using Counter

What’s Next?

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