Just one problem (at least) with the [color=rgb(40,40,40);font-family:helvetica, arial, sans-serif;]PCF8574 code - the device address is 0x20 not 0x38.[/color]
[color=rgb(40,40,40);font-family:helvetica, arial, sans-serif;]([/color]http://www.ti.com/li...ink/pcf8574.pdf page 4)
[color=rgb(40,40,40);font-family:helvetica, arial, sans-serif;]If you write and no device is there you should see the address sent out.[/color]
Yes, you are right.
But pay attention there is a device with 'A' postfix: PCF8574A, it has 0x38 base address: