Hallo David,

evtl. hilft Dir ja das folgende kleine Progr.
Mega8 + PCF8574 + 8 LED's an dessen Port's.

Code:
$regfile = "m8def.dat"                       'ATmega8-Deklarationen
$crystal = 3686400                           'Quarz: 3,6864 MHz
$baud = 9600                                 'Baudrate zum PC: 9600 Baud
'
Config Sda = Portc.4                         'ist für I2C erforderlich
Config Scl = Portc.5                         'dito

'...............................................................................

Const Pcfled = &H40                          'Adresses PCF8574 0.0.0


'BITMUSTER LED
Const Led_0 = &B00000001                     'PCF Port 0 ein
Const Led_1 = &B00000010                     'PCF Port 1 ein
Const Led_2 = &B00000100                     'PCF Port 2
Const Led_3 = &B00001000                     'PCF Port 3
Const Led_4 = &B00010000                     'PCF Port 4
Const Led_5 = &B00100000                     'PCF Port 5
Const Led_6 = &B01000000                     'PCF Port 6
Const Led_7 = &B10000000                     'PCF Port 7
Const Led_blank = &B00000000                 'alle LED aus


' --- Programmoperationen ------------------------------------------------------

I2cinit                                      'I2C Bus initialisieren

Do
   I2cstart                                  'Bus starten
   I2cwbyte Pcfled                           'Addresse PCF senden

   I2cwbyte Led_0                            'LED-Bitmuster senden
   Wait 2

   I2cwbyte Led_1                            'LED-Bitmuster senden
   Wait 2

   I2cwbyte Led_2                            'LED-Bitmuster senden
   Wait 2

    I2cwbyte Led_3                           'LED-Bitmuster senden
   Wait 2

   I2cwbyte Led_4                            'LED-Bitmuster senden
   Wait 2

   I2cwbyte Led_5                            'LED-Bitmuster senden
   Wait 2

   I2cwbyte Led_6                            'LED-Bitmuster senden
   Wait 2

   I2cwbyte Led_7                            'LED-Bitmuster senden
   Wait 2

   I2cwbyte Led_blank                        'LED-Bitmuster senden
   Wait 2

   I2cstop                                   'Bus wieder freigeben
Loop

End                                          'end program
mfg Gerhard