RE: [Lcd4linux-devel] connecting i2c lcd

[Luis.F.Correia <Lui...@se...>]

Hi! 

> -----Original Message-----
> From: paul kamphuis [mailto:pau...@xs...] 
> Sent: Monday, February 14, 2005 7:51 AM
> To: lcd...@li...
> Subject: [Lcd4linux-devel] connecting i2c lcd
> 
> Hi,
> 
> First things first, my quick test last friday didn't work! Besides it 
> would have been to easy if it worked just like this.
> 
> To investigate it a little further, I also did a test with a pcf8574 
> driving some led's. (Sometimes you are just lucky to have 
> something like 
> that available). I used the following piece of C code to test it.
> 
> char buf[1];
> buf[0] = 4;
> file = open("\sys\bus\i2c\devices\0-0020\write",O_WRONLY);
> write(file,buf,1)
> 
> At power up the leds outputs are clearly in an undefined 
> state (some on, 
> some off) After running the above code all led's go off. So there is 
> activity, but not the desired. (note the strange code of 4 to 
> turn on a 
> led. There are 19 led's connected so it is encoded.)
> 
> There is a different way to access a device, and it goes like this 
> through the command line:
> 
> $ echo 4 > \sys\bus\i2c\devices\0-0020\write
> This correctly turns on the desired led.

For all that I know, this is the best way to drive something connected to a
/sys/bus interface.

All other methods should be used programatically.

> Is there anyone who has an idea of the difference between the 
> C code and 
> the command line?

Try to write some C code using the I2C api.

> 
> Paul
> 

Luis