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zeronix
Joined: 08 Jun 2010
Posts: 9
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| i2c Problem |
 Posted: Sat Oct 16, 2010 6:48 pm |
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Hi Folks.. 
I'm working on a project that uses an accelerometer with i2c communication.
The Accelerometer works well with a 1,5meters cable (rs482 multifillar cable).
Recently I bought an 4meter IDC cable to substitute the old one. I can't communicate with accelerometer with the new one!
Any suggestions/tips to increase communication distance on i2c ?
I have tried increase and decrease the pull up resistance and used fast/standard without sauces!
Regards,
José |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sat Oct 16, 2010 9:22 pm |
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Use stronger pull-ups (1.6K for a +5v system). Slow down the baud rate.
Try using less than a 50 KHz baud rate. Try using software i2c (no
"Force_hw" parameter in #use i2c). |
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zeronix
Joined: 08 Jun 2010
Posts: 9
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| Posted: Sat Oct 16, 2010 9:48 pm |
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| PCM programmer wrote: | Use stronger pull-ups (1.6K for a +5v system). Slow down the baud rate.
Try using less than a 50 KHz baud rate. Try using software i2c (no
"Force_hw" parameter in #use i2c). |
Hi thks for response.
I already try 1k, 2.2k , 8.x k , 20.xk and with 0k :=) with no result!
I will try tomorrow slow down like you said
Where in the #use i2c i change the speed of communication?
My code :
| Code: | #include <18f2550.h>
#fuses HSPLL,NOWDT,NOBROWNOUT,NOPROTECT,NOLVP,NODEBUG,USBDIV,PLL5,CPUDIV1,VREGEN,MCLR,NOPBADEN,WRTB,CPB
#use delay(clock=48000000)
#define Device_SDA PIN_B0 // Pin defines i2c serial data e serial clock
#define Device_SCL PIN_B1
#use i2c( master,fast, sda=PIN_B0, scl=PIN_B1) // Configure Device as Master i2c fast mode |
Regards, |
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zeronix
Joined: 08 Jun 2010
Posts: 9
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| Posted: Sun Oct 17, 2010 9:38 pm |
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| PCM programmer wrote: | Use stronger pull-ups (1.6K for a +5v system). Slow down the baud rate.
Try using less than a 50 KHz baud rate. Try using software i2c (no
"Force_hw" parameter in #use i2c). |
Hi again,
I tried all day to put the i2c cable to work but without success.
I use the parameter that you recommend but without success.
Close the board works perfectly but with my 4m idc cable don't work at all :( (Probably I have to buy a better cable, I didn´t know of that this limitation on cable length in i2c)
I use that code:
| Code: | | #use i2c( master,sda=PIN_B0, scl=PIN_B1,slow, FORCE_HW) |
It is possible to slow I2C baudrate giving for example in slow a parameter like slow= 10000?
Sorry to bother you.
Regards, |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sun Oct 17, 2010 10:10 pm |
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Use software i2c and slow it down. Example:
| Code: |
#use i2c(master, sda=PIN_B0, scl=PIN_B1, slow=40000) |
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rnielsen
Joined: 23 Sep 2003
Posts: 852
Location: Utah
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| Posted: Mon Oct 18, 2010 8:59 am |
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I had a similar problem with a long distance and I needed to abandon using the built in functions and had to bit-bang the I2C bus. It took a bit of work controlling the tris so I didn't get erroneous spikes on the bus but I have one working at 32 feet.
Ronald |
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bkamen
Joined: 07 Jan 2004
Posts: 1615
Location: Central Illinois, USA
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| Posted: Mon Oct 18, 2010 9:38 am |
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Make sure you have the I2C Specs (if I haven't mentioned it already) -- I have a copy (albeit old, but I think current) here: http://www.benjammin.net/~bkamen/pdf/i2c-specification-v2.1-jan2000.pdf
While there isn't a max length spec, longer cables/lines will lead to changes in transmission characteristics that alter timing -- and that is critical (and mentioned in the PDF).
Cheers,
-Ben
_________________
Dazed and confused? I don't think so. Just "plain lost" will do. :D |
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