All,

After I shot myself 5 times in the head (and one time in the foot), I still found the energy to write a last message regarding this subject...

Erik, you were (once again) right from the beginning! You must be one of the 'white ravens' out there (at least, in the 8051 area...). ;-)

Let me tell what the problem was:

As told and said and shown in the code, I wanted to use pin0 as input and all the rest as output.
I used pin6 to control a LED.

Now what happened was: When I pressed the button down, the level of pin0 was '0'. So, when I read the byte, I got the value 0x40 back.
Due to that, I wanted to write a '0' to pin6 too, to activate the LED.
So, I had to write a complete byte back to the IO expander, with value 0x00 in this case.

BUT!!! Since pin0 was an input, I was not allowed to write '0' to pin0. I was 200% sure that I prevented the pins defined as input from being written with '0', because I was using a mask that defined the pins defined as inputs.

However, I was storing the mask inside a variable in my 8574 structure that was at last not holding the correct mask anymore.
So, when I read 0x40 because the key was pressed ('0' at input of pin0), I stored 0x40 in the buffer => gone mask!!!.

Solution: added an extra field to the struct that only saveguards a mask defining the input pins of that device.
Now, when I'm finished with the shifting, the bitwise "OR"-ing and the inversion, I bitwise "OR" again the result with the mask (this one never changes anymore).
Because of that, the bits representing the inputs are set to '1' again.

Sorry guys for:

• bothering you with such a stupid mistake
  
• taking your valuable time
  
• annoying you with a problem that wasn't a problem
  
• keeping you away from your family lives while reading this (in the mean time) long thread
  
• making some people 'angry' because of my not-so-optimal code
  

...and sorry to my cat Spooky for chasing her off of my keyboard this morning...
Here's a picture of her:



Now I can continue to drop dead... RIP... Sih!

Best rgds,

--Geert