Hm also irgendwo muss ich noch einen Denkfehler haben.
Folgendes Anschlussschemata (am mega8, keinen externen Oszillator oder ähnliches; Intern 1MHz)

LCD-PIN........Bezeichnung..........Anschluss
1..................Gnd.......................Gnd
2..................Vcc........................Vcc
3..................Vee.......................Vee (am Poti)
4..................RS.........................PC4
5..................R/W.......................PD0 (RXD)
6..................Enable....................PC5
7.
8.
9.
10.
11................DB4.......................PC0
12................DB5.......................PC1
13................DB6.......................PC2
14................DB7.......................PC4

main.c

Code:
#include <stdlib.h>
#include <avr/io.h>

#include "lcd.c"



int main(void)
{
    lcd_init(LCD_DISP_ON);
    lcd_clrscr();
    for (;;){
     lcd_puts("Test");
    }
return 0;
}
lcd.h
Code:
#ifndef LCD_H
#define LCD_H
/*************************************************************************
 Title	:   C include file for the HD44780U LCD library (lcd.c)
 Author:    Peter Fleury <pfleury@gmx.ch>  http://jump.to/fleury
 File:	    $Id: lcd.h,v 1.13.2.2 2006/01/30 19:51:33 peter Exp $
 Software:  AVR-GCC 3.3
 Hardware:  any AVR device, memory mapped mode only for AT90S4414/8515/Mega
***************************************************************************/

/**
 @defgroup pfleury_lcd LCD library
 @code #include <lcd.h> @endcode
 
 @brief Basic routines for interfacing a HD44780U-based text LCD display

 Originally based on Volker Oth's LCD library,
 changed lcd_init(), added additional constants for lcd_command(), 
 added 4-bit I/O mode, improved and optimized code.
       
 Library can be operated in memory mapped mode (LCD_IO_MODE=0) or in 
 4-bit IO port mode (LCD_IO_MODE=1). 8-bit IO port mode not supported.

 Memory mapped mode compatible with Kanda STK200, but supports also 
 generation of R/W signal through A8 address line.
       
 @author Peter Fleury pfleury@gmx.ch http://jump.to/fleury
 
 @see The chapter Interfacing a HD44780 Based LCD to an AVR
      on my home page.

*/

/*@{*/

#if (__GNUC__ * 100 + __GNUC_MINOR__) < 303
#error "This library requires AVR-GCC 3.3 or later, update to newer AVR-GCC compiler !"
#endif

#include <inttypes.h>
#include <avr/pgmspace.h>

/** 
 *  @name  Definitions for MCU Clock Frequency
 *  Adapt the MCU clock frequency in Hz to your target. 
 */
#define XTAL 8000000              /**< clock frequency in Hz, used to calculate delay timer */

/**
 * @name  Definition for LCD controller type
 * Use 0 for HD44780 controller, change to 1 for displays with KS0073 controller.
 */
#define LCD_CONTROLLER_KS0073 0  /**< Use 0 for HD44780 controller, 1 for KS0073 controller */

/** 
 *  @name  Definitions for Display Size 
 *  Change these definitions to adapt setting to your display
 */
#define LCD_LINES           2     /**< number of visible lines of the display */
#define LCD_DISP_LENGTH    16     /**< visibles characters per line of the display */
#define LCD_LINE_LENGTH  0x40     /**< internal line length of the display    */
#define LCD_START_LINE1  0x00     /**< DDRAM address of first char of line 1 */
#define LCD_START_LINE2  0x40     /**< DDRAM address of first char of line 2 */
#define LCD_START_LINE3  0x14     /**< DDRAM address of first char of line 3 */
#define LCD_START_LINE4  0x54     /**< DDRAM address of first char of line 4 */
#define LCD_WRAP_LINES      0     /**< 0: no wrap, 1: wrap at end of visibile line */


#define LCD_IO_MODE      1         /**< 0: memory mapped mode, 1: IO port mode */
#if LCD_IO_MODE
/**
 *  @name Definitions for 4-bit IO mode
 *  Change LCD_PORT if you want to use a different port for the LCD pins.
 *
 *  The four LCD data lines and the three control lines RS, RW, E can be on the 
 *  same port or on different ports. 
 *  Change LCD_RS_PORT, LCD_RW_PORT, LCD_E_PORT if you want the control lines on
 *  different ports. 
 *
 *  Normally the four data lines should be mapped to bit 0..3 on one port, but it
 *  is possible to connect these data lines in different order or even on different
 *  ports by adapting the LCD_DATAx_PORT and LCD_DATAx_PIN definitions.
 *  
 */
#define LCD_PORT         PORTC        /**< port for the LCD lines   */
#define LCD_DATA0_PORT   LCD_PORT     /**< port for 4bit data bit 0 */
#define LCD_DATA1_PORT   LCD_PORT     /**< port for 4bit data bit 1 */
#define LCD_DATA2_PORT   LCD_PORT     /**< port for 4bit data bit 2 */
#define LCD_DATA3_PORT   LCD_PORT     /**< port for 4bit data bit 3 */
#define LCD_DATA0_PIN    0            /**< pin for 4bit data bit 0  */
#define LCD_DATA1_PIN    1            /**< pin for 4bit data bit 1  */
#define LCD_DATA2_PIN    2            /**< pin for 4bit data bit 2  */
#define LCD_DATA3_PIN    3            /**< pin for 4bit data bit 3  */
#define LCD_RS_PORT      LCD_PORT     /**< port for RS line         */
#define LCD_RS_PIN       4            /**< pin  for RS line         */
#define LCD_RW_PORT      PORTD     /**< port for RW line         */
#define LCD_RW_PIN       0            /**< pin  for RW line         */
#define LCD_E_PORT       LCD_PORT     /**< port for Enable line     */
#define LCD_E_PIN        5            /**< pin  for Enable line     */

#elif defined(__AVR_AT90S4414__) || defined(__AVR_AT90S8515__) || defined(__AVR_ATmega64__) || \
      defined(__AVR_ATmega8515__)|| defined(__AVR_ATmega103__) || defined(__AVR_ATmega128__) || \
      defined(__AVR_ATmega161__) || defined(__AVR_ATmega162__)
/*
 *  memory mapped mode is only supported when the device has an external data memory interface
 */
#define LCD_IO_DATA      0xC000    /* A15=E=1, A14=RS=1                 */
#define LCD_IO_FUNCTION  0x8000    /* A15=E=1, A14=RS=0                 */
#define LCD_IO_READ      0x0100    /* A8 =R/W=1 (R/W: 1=Read, 0=Write   */
#else
#error "external data memory interface not available for this device, use 4-bit IO port mode"

#endif
...
REST Unverändert gelassen
Müsste doch so eigentlich funktionieren oder? Ich habe selbst in der Makefile einmal F_CPU auf 1000000 und auch XTAL auf 1000000 (aus der lcd.h) gesetzt (müsste es eigentlich nicht 1000000UL heißen?), hat aber keinen Effekt - das Display bleibt schwarz.
Viele Grüße,
Simon