I have used the PCF8574 driver that was provided here: viewtopic.php?f=41&t=916

Writing to the PCF8574 is no problem at all. But if I read a button the application crashes most of the time.

what I do is quite simple and straight forward:
- connecting 4 LED's to P0 - P3
- connecting a button between Pin 9 (P4) and ground



That should do the job, one would think. But it crashes quite often. Adding a Wait1Msec(1500); or so doesn't help either.

It seems that if I modify the code to this is seems to work better:
I have used the PCF8574 driver that was provided here: viewtopic.php?f=41&t=916
Writing to the PCF8574 is no problem at all. But if I read a button the application crashes most of the time.

what I do is quite simple and straight forward:
- connecting 4 LED's to P0 - P3
- connecting a button between Pin 9 (P4) and ground



It seems to be that the latter code works better, but still crashes if I keep the button pushed. What is the cause of this behaviour?!

Hi JopieK,

Sorry its been a long time since I have logged in, I will take a look at the code and see what I can do. I'm surprised it is crashing when reading the button. Ill see what I can do B-)

Scott B-)

Quick Question, when the application crashes, does the NXT freeze or does it print an error to the screen?

If it prints an error to the screen I know whats going on. I wrote a error function that checks the hardware pins to make sure the hardware pins are the same as the message sent. However I didn't think if one of the pins is hooked to a switch, it could be a 1 or 0, which would make the hardware check fail lol. I suggest deleting the function code in PCF8574Error, and leaving it an empty function. This should fix your problem B-)

Also, I took a look at my driver and remembered that PCF8574PinRead returns a 1 if the pin is high, and a 0 if the pin is low. You are comparing this to 5, It still works because 5 != 0 making it true, but just fyi.

Sorry for all the problems, and good luck with your project B-)
Scott