This is the Article to introduce the Timer programming of ARM Cortex-M3 LPC1768 Microcontroller. Here we are going to initialize the timer peripheral in LPC1768. Timer will improve the way of usage of any microcontroller. In this tutorial we are going to set up two timers which will blink two LEDs according to the setting of the timers. Setting up the Environment for the development of ARM cortex M3 is well discussed in this article.

The LPC 1768 is ARM Cortex- M3 based Microcontrollers for embedded application features in low power consumption and a high level of integration. The ARM Cortex M3 is designed in a such way to enhance debug features and a higher level of system integration. It clocks at a CPU frequency of 100 MHz, and incorporates a 3-stage pipeline and uses a Harvard architecture with separate local instruction and data buses for third bus peripherals. The ARM Cortex- M3 CPU have an internal pre-fetch unit to support speculative branching. The peripheral components include 512KB of flash memory, 64kb of data memory, Ethernet MAC, USB OTG, 4 UART’s, 8-channel general purpose DMA controller, 2 SSP Controllers, 10-bit DAC, Quadrature encoder interface, SPI interface, 3 I2C bus interface, 2 input plus 2 outputs I2S bus interface, 4 general purpose timers, ultra-low power Real-Time Clock (RTC) with separate battery supply, and up to 70 general purpose I/O pins, 6-output general purpose PWM. The LPC1768/66/65/64 are pin-compatible with the 100-pin LPC236x ARM7-based Microcontroller series.

There are 4 timers in LPC1768 (0, 1, 2 and 3). Each has 32-bit timer/counter with programmable 32-bit prescaler. All are independently identical and can be used separately without any interference. Each has its Timer Counter (TC) which is 32bit register which will incremented according to the clock connected up and there is a prescale counter which act as a clock divider.

Each Peripheral in LPC1768 can be turned ON or OFF according to our use, where most of the peripherals are turned off on reset. So the first step in any peripheral initialization is to turn on the peripheral.

Powering the Timers:

Conservation of power is the major concern in the LPC1768. Each peripheral has to turn ON before utilizing it. RESET makes some peripherals to enable while others are disabled. In timers Timer/Counters 0 and 1 are enabled while Timer/Counters 2 and 3 are disabled.

Fig. 1: Bit Configuration of Peripherals on reset in LPC1768

Here for TIMER1 and TIMER2 the power bit PCTIM0 and PCTIM1 must be set.

Code Snippet:

LPC_SC->PCONP |= (0x01<<1); //enable POWER to TIMER0

LPC_SC->PCONP |= (0x1<<2); // enable POWER to TIMER1

The Timer Peripheral Clock:

The following table specifies the relationship between the peripherals and the bits in the PCLKSEL0 and PCKSEL1 registers.

Fig. 2: Peripheral Clock Selection Register 0 (PCLKSEL0) in PLC1768

Fig. 3: Peripheral Clock Selection Register 1 (PCLKSEL1) IN LPC1768

Example. Set the peripheral clock for timer 0 to divide by 8 of the system clock frequency.

pclkdiv = (LPC_SC->PCLKSEL0 >> 2) & 0x03;

switch ( pclkdiv )

{

case 0x00:

default:

pclk = SystemFrequency/4;

break;

case 0x01:

pclk = SystemFrequency;

break;

case 0x02:

pclk = SystemFrequency/2;

break;

case 0x03:

pclk = SystemFrequency/8;

break;

}

Enabling the timer:

The final step in the configuration is to enable the timer via the Timer Control Register (TCR):

Fig. 4: Bit Value Of Tmer Control Register For Enabling Timer In LPC1768

To reset and enable timer the code will be and similar to all the timer:

Code Snippet:

LPC_TIM0->TCR = 0x02;                 /* reset timer */

LPC_TIM0->TCR = 0x01;                 /* start timer */

In this section, we will start creating a project in Keil MDK we have already installed Keil µVision and Co-MDK Plug-in + CoLinkEx Drivers required for the CoLinkEx programming adapter. You can start by downloading the project files and kick start your practical experiment.

Code.rar

Code Description:

ARM programming requires good handling of Bit manipulation in C language. Here is the small note in the introduction of Bit manipulation to a newbie. C has direct support for bitwise operations that can be used for bit manipulation. In the following examples, n is the index of the bit to be manipulated within the variable bit_fld, which is an unsigned char being used as a bit field. Bit indexing begins at 0, not 1. Bit 0 is the least significant bit.

Set a bit

bit_fld |= (1 << n)

Clear a bit

bit_fld &= ~(1 << n)

Toggle a bit

bit_fld ^= (1 << n)

Test a bit

bit_fld & (1 << n)

timertest.c is the code to test the function of timer in the above given project as the functions are written in timer.c.

for ( i = 0; i < 2; i++ )

{

init_timer( i , TIME_INTERVAL );

enable_timer( i );

}

The above function is to initialize the Timers 0 and 1.

In while loop function each timer has its own timer counter variable which is compared to the desired blink interval and the LEDs are turned ON or OFF.

Project Source Code

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 The codes are linked in Description ###

Circuit Diagrams

Circuit-Diagram-Timers-Programming-in-LPC1768

Project Components

Project Video

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Filed Under: ARM, Featured Contributions

 

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