LPC1768 and UART PCLK

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Athul
Posts: 12
Joined: Thu Apr 07, 2016 1:00 am

LPC1768 and UART PCLK

Post by Athul » Wed Apr 18, 2018 1:32 am

I've been trying to configure UART module of LPC1768. Board comes with a crystal oscillator of 12Mhz. It does nothing more than receiving a character and transmitting it at the same time. I am using Keil simulator.
This is the code,

Code: Select all

#include <LPC17xx.H>

void uart_init()
{
    LPC_PINCON->PINSEL0 = 0X0500000;
    LPC_UART2->LCR = 0X83;
    LPC_UART2->DLL = 162;
    LPC_UART2->LCR = 0X03;
}

int main()
{
    uart_init();

    while(1)
    {
        while(LPC_UART2->LSR & (1<<0));
        LPC_UART2->THR = LPC_UART2->RBR;
        while(LPC_UART2->LSR & (1<<6));
    }
}
I'm not configuring any PLL register, only using default values.

I"ve referred several forums to find the baud rate, https://www.google.co.in/search?q=lp176 ... e&ie=UTF-8

By referring system_LPC17xx.c,

Code: Select all

#define CLOCK_SETUP           1
#define SCS_Val               0x00000020
#define CLKSRCSEL_Val         0x00000001
#define PLL0_SETUP            1
#define PLL0CFG_Val           0x00050063
#define PLL1_SETUP            1
#define PLL1CFG_Val           0x00000023
#define CCLKCFG_Val           0x00000003
#define USBCLKCFG_Val         0x00000000
#define PCLKSEL0_Val          0x00000000
#define PCLKSEL1_Val          0x00000000
#define PCONP_Val             0x042887DE
#define CLKOUTCFG_Val         0x00000000
From #define PLL0CFG_Val 0x00050063,

Bit 14-0 supplies the M value, and the value stored here is M-1; 0x0063 which is 99 in decimal, So M = 100,

Bit 23-16 Supplies the value "N", The value stored here is N - 1; 0x05=5 in decimal, so N = 6

From #define CCLKCFG_Val 0x00000003,

Bit 7-0, Selects the divide value for creating the CPU clock (CCLK), By putting a value of 3, CCLK = PLLCLK/4

I'm using UART2, which comes under PCLKSEL2,

From #define PCLKSEL2_Val 0x00000000,

when set 0, PCLK_peripheral = CCLK/4

TO find PLL0 freq, PLL0_clk = (2 * M * FOSC) / N ==>PLL0_clk = (2 * 100 * 12)/6 ==>PLL0_clk = 400Mhz

Now, CCLK = PPL0_clk/4 ==>CCLK = 400 / 4 = 100Mhz

and PCLK = CCLK/4 = 100/4 = 25Mhz

To calculate DLL, DLL = PCLK/(16 * Baud rate) for 9600 Bpm, DLL = 25000000/(16 * 9600) ==>DLL = 162

But I can't transmit or receive anything when I tried to simulate the program I've only limited knowledge in ARM, that's why I wrote my calculation method so that anyone can correct me if I'm wrong.??

Did I make any mistakes in cofiguring UART or PCLK??

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