So, hallo ich bins nochmal.

Ich hab den Code jetzt etwas umgeändert um die Zeichen in ein Array zu schreiben. Das Schreiben scheint auch zu funktionieren, da ich über Debugausgaben herasugefunden hab dass er diese Schleife in der ISR abarbeitet. Allerdings soll der Inhalt des Arrays in main an den PC geschickt werden. Das funktioniert leider nicht...

Hier mal mein aktueller Code für die Variante mit dem Array:

Code:
#include <c8051F330.h>
#include <stdio.h>

#define SYSCLK			24500000
#define BAUDRATE		115200
#define RX_length		25

//-----------------------------------------------------------------------------
// Global Variables
//-----------------------------------------------------------------------------

//bit TX_ready;						//True = OK zur Übertragung
//char *TX_ptr;						//pointer auf zu übermittelnden String

bit RX_ready;						//True = string empfangen

volatile char RX_buf[RX_length];				//Array als Eingangsbuffer anlegen

volatile unsigned char the_char;				//zwischenspeicher


sfr  SBUF = 0x99;


//-----------------------------------------------------------------------------
// Function Prototypes
//-----------------------------------------------------------------------------

void OSCILLATOR_Init (void);
void UART0_Init (void);
void PORT_Init (void);
void UART0_ISR (void);
void Print_String (char pstring[]);
char nb_getkey ();
char b_getkey ();

//-----------------------------------------------------------------------------
// main Routine
//-----------------------------------------------------------------------------
void main (void)
{
	
	int i;
	// Disable Watchdog timer
   	PCA0MD &= ~0x40;                    // WDTE = 0 (clear watchdog timer
                                       // enable)
   	OSCILLATOR_Init ();                 // Initialize Oscillator
	PORT_Init();                        // Initialize Port I/O
	UART0_Init ();						// Initialize UART0

	EA = 1;								//Interrupts global freigeben
	ES0 = 1;							//UART0 interrupt freigeben
	RI0=0;
	
	while(1)
	{
		if (RX_ready != 0)
		{
			for(i=0;putchar(RX_buf[i])!='\0';i++);
			RX_ready = 0;
		}
		
		 
	}

}

//-----------------------------------------------------------------------------
// Initialization Subroutines
//-----------------------------------------------------------------------------

//-----------------------------------------------------------------------------
// OSCILLATOR_Init
//-----------------------------------------------------------------------------
//
// Return Value : None
// Parameters   : None
//
// This routine initializes the system clock to use the internal 24.5MHz
// oscillator as its clock source.  Also enables missing clock detector reset.
//
//-----------------------------------------------------------------------------
void OSCILLATOR_Init (void)
{
   OSCICN |= 0x03;                     // Configure internal oscillator for
                                       // its maximum frequency
   RSTSRC  = 0x04;                     // Enable missing clock detector
}

//-----------------------------------------------------------------------------
// PORT_Init
//-----------------------------------------------------------------------------
//
// Return Value : None
// Parameters   : None
//
// P0.4    digital    push-pull     UART TX
// P0.5    digital    open-drain    UART RX
//
//-----------------------------------------------------------------------------
void PORT_Init (void)
{
   P0SKIP  |= 0x01;                    // Skip P0.0 for external VREF
   P1MDIN  |= 0xEF;                    // Configure P1.4 as analog input.
   P0MDOUT |= 0x10;                    // enable UTX as push-pull output
   XBR0    = 0x01;                     // Enable UART on P0.4(TX) and P0.5(RX)
   XBR1    = 0x40;                     // Enable crossbar and weak pull-ups
}

//-----------------------------------------------------------------------------
// UART0_Init
//-----------------------------------------------------------------------------
//
// Return Value : None
// Parameters   : None
//
// Configure the UART0 using Timer1, for <BAUDRATE> and 8-N-1.
//
//-----------------------------------------------------------------------------
void UART0_Init (void)
{
   SCON0 = 0x10;                       // SCON0: 8-bit variable bit rate
                                       //        level of STOP bit is ignored
                                       //        RX enabled
                                       //        ninth bits are zeros
                                       //        clear RI0 and TI0 bits
   if (SYSCLK/BAUDRATE/2/256 < 1) {
      TH1 = -(SYSCLK/BAUDRATE/2);
      CKCON &= ~0x0B;                  // T1M = 1; SCA1:0 = xx
      CKCON |=  0x08;
   } else if (SYSCLK/BAUDRATE/2/256 < 4) {
      TH1 = -(SYSCLK/BAUDRATE/2/4);
      CKCON &= ~0x0B;                  // T1M = 0; SCA1:0 = 01
      CKCON |=  0x09;
   } else if (SYSCLK/BAUDRATE/2/256 < 12) {
      TH1 = -(SYSCLK/BAUDRATE/2/12);
      CKCON &= ~0x0B;                  // T1M = 0; SCA1:0 = 00
   } else {
      TH1 = -(SYSCLK/BAUDRATE/2/48);
      CKCON &= ~0x0B;                  // T1M = 0; SCA1:0 = 10
      CKCON |=  0x02;
   }

   TL1 = TH1;                          // Init Timer1
   TMOD &= ~0xf0;                      // TMOD: timer 1 in 8-bit autoreload
   TMOD |=  0x20;
   TR1 = 1;                            // START Timer1
   TI0 = 1;                            // Indicate TX0 ready
}


void UART0_ISR (void) interrupt 4 using 3
{
	
	unsigned char RX_index = 0;				//zwischenspeicher

	if(RI0 == 1)
	{
		
		if(RX_ready != 1)
		{
			the_char = SBUF0;
			
			if(the_char != '\n' && ( RX_index < (RX_length-1)) )
			{
				
				RX_buf[RX_index] = the_char;
				RX_index++;
				RI0 = 0;
			}
			else
			{
				RX_buf[RX_index] = '\0';
				RX_index = 0;
				RX_ready = 1;
				RI0 = 0;
			}
		}
	
	}

}
Grüße!

Bean