So, ich habe mal mit diesen Programmen getestet:

RP6 Base (Slave):
Code:
/* 
 * ****************************************************************************
 * RP6 ROBOT SYSTEM - ROBOT BASE TESTS
 * ****************************************************************************
 * Example: I2C Slave - I2C Receive Test
 * Author(s): D. Ottensmeyer
 * ****************************************************************************
 * Description:
 *
 * This Example receives data via I2C as slave.
 *
 *
 * ############################################################################
 * The Robot does NOT move in this example! You can simply put it on a table
 * next to your PC and you should connect it to the PC via the USB Interface!
 * ############################################################################
 * ****************************************************************************
 */

/*****************************************************************************/
// Includes:

#include "RP6RobotBaseLib.h"	// The RP6 Robot Base Library. 
								// Always needs to be included!
#include "RP6I2CTWI.h"			// Include the new I2C-Bus Library

/*****************************************************************************/
// Defines:

// The Slave Address on the I2C Bus can be specified here:
#define RP6BASE_I2C_SLAVE_ADR 10

#define CMD_SHOW_DATA 99		// Command to display the data

#define TEXT_OUTPUT				// Show text

/*****************************************************************************/
// Variables:

uint16_t cnt = 0;
uint16_t error_cnt = 0;
uint8_t controlbyte; 
uint8_t highbyte = 0; 
uint8_t lowbyte = 0; 

/*****************************************************************************/
// Main function - The program starts here:

int main(void)
{ 

	initRobotBase(); 

	setLEDs(0b111111);
	mSleep(500);	   
	setLEDs(0b000000);

	I2CTWI_initSlave(RP6BASE_I2C_SLAVE_ADR); 
    
	while (true) 
	{    
		if (I2CTWI_writeRegisters[0] && !I2CTWI_writeBusy) { 
			controlbyte = I2CTWI_writeRegisters[0];		// Read control byte
			I2CTWI_writeRegisters[0] = 0;				//  and reset it (!!!)
			lowbyte = I2CTWI_writeRegisters[1];			// Read lowbyte 
			highbyte = I2CTWI_writeRegisters[2];		// Read highbyte 
			if (controlbyte == CMD_SHOW_DATA) { 
				cnt = ((highbyte << 8) | lowbyte);		// Restore 16-bit value 
#ifdef TEXT_OUTPUT
				writeString_P("Received: ");			//  and show it
				writeInteger(cnt, DEC);
#endif
				if (!cnt) error_cnt = 0;				// Reset error counter
				else error_cnt++;						// Error counter + 1
				if (cnt != error_cnt) {
					writeString_P(" ERROR!\n");
					error_cnt = cnt;
				}
#ifdef TEXT_OUTPUT
				else writeChar('\n');
#endif
				controlbyte = 0;
			}
		}
	} 
	return 0;
}

/******************************************************************************
 * Additional info
 * ****************************************************************************
 * Changelog:
 * - v. 1.0 (initial release) 19.02.2011 by D. Ottensmeyer
 *
 * ****************************************************************************
 */

/*****************************************************************************/
RP6 M32 (Master):
Code:
/* 
 * ****************************************************************************
 * RP6 ROBOT SYSTEM - RP6 CONTROL M32 EXAMPLES
 * ****************************************************************************
 * Example: I2C Master - I2C Send Test
 * Author(s): D. Ottensmeyer
 * ****************************************************************************
 * Description:
 *
 * This Example sends data via I2C as master.
 *
 *
 * ############################################################################
 * The Robot does NOT move in this example! You can simply put it on a table
 * next to your PC and you should connect it to the PC via the USB Interface!
 * ############################################################################
 * ****************************************************************************
 */

/*****************************************************************************/
// Includes:

#include "RP6ControlLib.h"	 	// The RP6 Control Library.
								// Always needs to be included!
#include "RP6I2CTWI.h"			// Include the new I2C-Bus Library

/*****************************************************************************/
// Defines:

// The Slave Address on the I2C Bus can be specified here:
#define RP6BASE_I2C_SLAVE_ADR 10

#define CMD_SHOW_DATA 99		// Command to display the data

#define TEXT_OUTPUT				// Show text

/*****************************************************************************/
// I2C Event handlers:

/**
 * This function gets called automatically if there was an I2C Error like
 * the slave sent a "not acknowledge" (NACK, error codes e.g. 0x20 or 0x30).
 * The most common mistakes are: 
 *   - using the wrong address for the slave
 *   - slave not active or not connected to the I2C-Bus
 *   - too fast requests for a slower slave
 * Be sure to check this if you get I2C errors!
 */
void I2C_transmissionError(uint8_t errorState)
{
	writeString_P("\nI2C ERROR --> TWI STATE IS: 0x");
	writeInteger(errorState, HEX);
	writeChar('\n');
}

/*****************************************************************************/
// Variables:

uint16_t cnt = 0;
uint8_t buffer[4];

/*****************************************************************************/
// Main - The program starts here:

int main(void)
{ 
	initRP6Control(); 

	initLCD(); 

	I2CTWI_initMaster(100); // Initialize the TWI Module for Master operation
							// with 100kHz SCL Frequency
	
	// Register the event handlers:
	I2CTWI_setTransmissionErrorHandler(I2C_transmissionError);

	setLEDs(0b1111);
	mSleep(500);	   
	setLEDs(0b0000);
	
	while(true)  
	{
		if (!I2CTWI_isBusy()) {
			cnt++;									// TEST: COUNTER!!!
			if (cnt > 32767) cnt = 0;
			buffer[0] = 0;
			buffer[1] = CMD_SHOW_DATA;
			buffer[2] = cnt;
			buffer[3] = (cnt >> 8);
			I2CTWI_transmitBytes(RP6BASE_I2C_SLAVE_ADR, buffer, 4);
#ifdef TEXT_OUTPUT
			setCursorPosLCD(0, 0); 
			writeStringLCD_P("I2C has sent:");		// What was sent? 
			setCursorPosLCD(1, 0); 
			writeIntegerLCD(cnt, DEC);
#endif
		}
	} 
	return 0; 
}

/******************************************************************************
 * Additional info
 * ****************************************************************************
 * Changelog:
 * - v. 1.0 (initial release) 19.02.2011 by D. Ottensmeyer
 *
 * ****************************************************************************
 */

/*****************************************************************************/
Ergebnis:
Der Zähler zählt immer 3 Stellen hoch, danach wird eine Stelle ausgelassen. Da pro Zähler 4 Bytes übertragen werden, flutschen wohl immer ca. 12 Bytes, bevor eins verloren geht.

Gruß Dirk

... ich bleibe dran ...