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i2c problem

 
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isikmurat06



Joined: 08 Jan 2011
Posts: 7

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i2c problem
PostPosted: Sat Jan 08, 2011 8:11 am     Reply with quote
hi,

I wanna communucate 3 pic with eacother.
One of them must be master and the others must be slave.
The LCD that is connected to slave pic doesn't show anything.
Please help....

I use this code for master pic;
Code:

#use i2c(master,sda=pin_c4,scl=pin_c3,fast=400000)
.
.
.
i.2c_start();
i2c_write(0x01); // slave pic address
i2c_write(data);
i2c_stop();
.
.
.

I use this code for slave pic;
Code:

#use i2c(slave,sda=pin_c4,scl=pin_c3,fast=400000,address=0x01,FORCE_HW)
.
.
.
#INT_SSP
int I2C_kesme()
{
   int data;
   disable_interrupts(INT_SSP);
   i2c_start();
   i2c_write(0x01);
   data=i2c_read();
   delay_ms(11);
   i2c_stop();
   printf(putc_lcd,"%d",data);
   return;
}
.
.
.
Ttelmah



Joined: 11 Mar 2010
Posts: 19552

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PostPosted: Sat Jan 08, 2011 9:41 am     Reply with quote
'1' is not a legitimate I2C address. The first few addresses are _reserved_, and an address number will always be _even_. The low bit of an I2C address is the 'direction' flag. You are sending a command to read from reserved device 0.

Best Wishes
Ttelmah



Joined: 11 Mar 2010
Posts: 19552

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PostPosted: Sat Jan 08, 2011 10:21 am     Reply with quote
Also, understand, that the _master_ controls all transactions. Only it can send a start or a stop.

Best Wishes
temtronic



Joined: 01 Jul 2010
Posts: 9246
Location: Greensville,Ontario

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PostPosted: Sat Jan 08, 2011 12:32 pm     Reply with quote
Also be sure to add pullups on the I2C lines ! 4K7r I think....
asmallri



Joined: 12 Aug 2004
Posts: 1635
Location: Perth, Australia

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PostPosted: Sat Jan 08, 2011 2:45 pm     Reply with quote
temtronic wrote:
Also be sure to add pullups on the I2C lines ! 4K7r I think....


1K for 400KHz, 4K7 for 100KHz
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Regards, Andrew

http://www.brushelectronics.com/software
Home of Ethernet, SD card and Encrypted Serial Bootloaders for PICs!!
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Sat Jan 08, 2011 3:03 pm     Reply with quote
The 1K value for 400 KHz is for 3.3v operation:
http://www.maxim-ic.com/app-notes/index.mvp/id/476
For a 5v system, it would be 1.6K to 1.7K minimum.
isikmurat06



Joined: 08 Jan 2011
Posts: 7

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PostPosted: Sun Jan 09, 2011 8:42 am     Reply with quote
thanks you all for your answer. I will try and share the results.
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