ReSiStAnCe:
When you look at the datasheet http://www.nxp.com/documents/data_sheet/PCF8574.pdf on page 10 you can see that the device-adress is 7 bits long.
Starting from A0,A1 and A2, then 0,0,1,0. So your adress is somewhere between b0100000 and b0100111 or between 0x20 and 0x27.
So if you set A0 - A1 low this is 0x20. You declare it as being 0x38. I assume the comment was not edited by you, so the original code adressed the device with A0 - A1 set high...
the chip i'm using is PCF8574 AP and the datasheet gives below value for the address:
For PCF8574A the addressing is:
A2 A1 A0 Dec Hex
L L L 56 0x38
L L H 57 0x39
L H L 64 0x40
L H H 74 0x4A
H L L 75 0x4B
H L H 76 0x4C
H H L 77 0x4D
H H H 78 0x4E