hello_world.c

#include <EFM8LB1.h>
#include <stdio.h>

#define SYSCLK      24500000L  // SYSCLK frequency in Hz
#define BAUDRATE      115200L  // Baud rate of UART in bps

char _c51_external_startup (void)
{
	// Disable Watchdog with key sequence
	SFRPAGE = 0x00;
	WDTCN = 0xDE; //First key
	WDTCN = 0xAD; //Second key
  
	VDM0CN |= 0x80;
	RSTSRC = 0x02;

	// Use a 24.5MHz clock
	SFRPAGE = 0x00;
	CLKSEL  = 0x00;
	CLKSEL  = 0x00;
	while ((CLKSEL & 0x80) == 0);
	
	P0MDOUT |= 0x10; // Enable UART0 TX as push-pull output
	XBR0     = 0x01; // Enable UART0 on P0.4(TX) and P0.5(RX)                     
	XBR1     = 0X00;
	XBR2     = 0x40; // Enable crossbar and weak pull-ups

	// Configure Uart 0
	SCON0 = 0x10;
	CKCON0 |= 0b_0000_1000 ; // Timer 1 uses the system clock.
	TH1 = 0x100-((SYSCLK/BAUDRATE)/2L);
	TL1 = TH1;      // Init Timer1
	TMOD &= ~0xf0;  // TMOD: timer 1 in 8-bit auto-reload
	TMOD |=  0x20;                       
	TR1 = 1; // START Timer1
	TI = 1;  // Indicate TX0 ready
	
	return 0;
}

void main (void) 
{
	printf( "Hello, world!\r\n" );
}