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mwildbolz
Joined: 26 Jul 2005
Posts: 16
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| I2C - Hang on I2C_write() |
 Posted: Tue Dec 13, 2005 2:35 pm |
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Hi!
Since a few days, i have a big problem.
When i process an i2c_write() command on my PIC 16F747 via the hardware I2C - Interface, the �C hangs!
I have no ideas, whats wrong with my controller or my schematic. An interesting fact was, that i had this problem already and i only was able to solve it, by creating a new PCB. And now, i have it again.
Does anybody know about this problem?
Pleas help me, it is really important! |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Tue Dec 13, 2005 2:56 pm |
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1. Post a very small (but complete) program that shows the problem.
Show all #include, #fuses, and #use statements.
2. Describe your hardware connections. Do you have pull-up
resistors on SDA and SCL ? What are the values of the resistors ?
3. What is your compiler version ? |
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asmallri
Joined: 12 Aug 2004
Posts: 1635
Location: Perth, Australia
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| Re: I2C - Hang on I2C_write() |
| Posted: Tue Dec 13, 2005 7:02 pm |
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| mwildbolz wrote: | Hi!
Since a few days, i have a big problem.
When i process an i2c_write() command on my PIC 16F747 via the hardware I2C - Interface, the �C hangs!
I have no ideas, whats wrong with my controller or my schematic. An interesting fact was, that i had this problem already and i only was able to solve it, by creating a new PCB. And now, i have it again.
Does anybody know about this problem?
Pleas help me, it is really important! |
Check your pull up resistors.
_________________
Regards, Andrew
http://www.brushelectronics.com/software
Home of Ethernet, SD card and Encrypted Serial Bootloaders for PICs!! |
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kender
Joined: 09 Aug 2004
Posts: 768
Location: Silicon Valley
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| Posted: Tue Dec 13, 2005 7:45 pm |
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Try adding these lines to you initialization code:
| Code: |
output_float(PIN_SCL);
output_float(PIN_SDA);
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mwildbolz
Joined: 26 Jul 2005
Posts: 16
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| Posted: Wed Dec 14, 2005 2:58 am |
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Hi!
My hardware is OK. I have installed pull up resistors and i have 5 Volts on SDA and SCL when the bus is idle.
The values of the resistors are 4k7
The code from my testing program:
| Code: |
#include <16F747.h>
//*******Configuration of the �C and the CCS Compiler********
#use delay(clock=12000000)
#fuses HS, PUT, NOPROTECT, NOBROWNOUT, BORV20, MCLR, NOFCMEN, NOIESO, NOBORSEN, NODEBUG
#use I2C(master,sda=PIN_C4,scl=PIN_C3, FORCE_HW, RESTART_WDT) //Routines for I2C
#use rs232(baud=9600, xmit=PIN_C6,rcv=PIN_C7) //Routines for RS232
//****************Global Definitions**************************
#define I2C_enabled True //Possibility to disable the I2C interface for testing
#define Debug True //Display debug messages throug RS232 interface for debugging purposes
#define EEPROM_write_active True //Disable writing to the EEPROM
//******************Function prototypes**********************
//**********************Includes****************************
#include "EEPROM.h"
//**************************void main***************************
void main()
{
I2C_Start();
printf("start fertig");
i2c_write(0xa0);
printf("Write fertig");
i2c_stop();
while(1)
{
}
}
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The line printf("Write fertig"); is never reached. The �C hangs on the i2c_write(). It doesn't matter, if the adressed device is physically available or not.
Compiler Version: PCWH 3.222
Btw: I wasn't able to try setting the PIN's floating. I can do this not before tomorrow.
greetings, Markus |
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treitmey
Joined: 23 Jan 2004
Posts: 1094
Location: Appleton,WI USA
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| Posted: Wed Dec 14, 2005 8:52 am |
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This compiles on 3.239 and ran to compleation on my hardware. Only a couple of changes. In the comments it says disable writing. Is this getting you hung up? | Code: | #include <18F452.H>
#CASE
#USE DELAY(CLOCK=40000000)
#FUSES H4,NOWDT,NOPROTECT,NOLVP
#DEFINE VER_MAJOR 2
#DEFINE VER_MINOR 01
#USE RS232(BAUD=19200,XMIT=PIN_C0,INVERT,STREAM=DEBUG,DISABLE_INTS) // STDERR(same as DEBUG)
#USE RS232(BAUD=19200,ENABLE=PIN_C5,XMIT=PIN_C6,RCV=PIN_C7,STREAM=RS485)
#use I2C(master,sda=PIN_C4,scl=PIN_C3, FORCE_HW, RESTART_WDT) //Routines for I2C
#define I2C_enabled True //Possibility to disable the I2C interface for testing
#define Debug True //Display debug messages throug RS232 interface for debugging purposes
#define EEPROM_write_active True //Disable writing to the EEPROM
void main()
{
i2c_start();
fprintf(DEBUG,"Start fertig\n\r");
i2c_write(0xa0);
fprintf(DEBUG,"Write fertig\n\r");
i2c_stop();
while(1)
{
}
}
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mwildbolz
Joined: 26 Jul 2005
Posts: 16
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| Protecting circuit for i2c Pins |
| Posted: Fri Dec 16, 2005 7:16 am |
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Hi there!
I hadn't tried your code, but i found the problem. It looks like the I2C Port of my �C is broken down.
I am not sure why, but if i take another controller of the same type, with the same program and the same PCB, it works fine.
Now, i am looking for a schematic, which protects my I2C Pins. Do you have any ideas?? Maybe it works with normal diodes (Zener Diodes) or has anyone a better idea for me??
Greetings, Markus |
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mwildbolz
Joined: 26 Jul 2005
Posts: 16
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| Posted: Sun Dec 18, 2005 5:42 am |
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Has nobody a good idea?? 
I need some ideas because i have to finish my work on this project 
Please help me.
Greetings, Markus |
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Storic
Joined: 03 Dec 2005
Posts: 182
Location: Australia SA
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| Posted: Sun Dec 18, 2005 7:30 am |
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A lot of circuits I have seen and used consists of a Zener, Buffer resistors and even Caps. 
try and have a look at http://www.maxim-ic.com/appnotes.cfm/appnote_number/564 it may help.
ANdrew
_________________
What has been learnt if you make the same mistake?  |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sun Dec 18, 2005 12:17 pm |
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| Quote: | | Now, i am looking for a schematic, which protects my I2C Pins. |
Get the Philips i2c spec, here:
http://www.semiconductors.philips.com/acrobat/literature/9398/39340011.pdf
On page 37 at the bottom right, they suggest using series resistors
to protect the i2c pins. On page 39, there is a schematic.
I haven't used these series resistors but in other circuits that I've seen,
most people seem to use 100 ohms.
After you put in the series resistors, you should look at the i2c pins
with an oscilloscope to make sure that they have the correct logic levels. |
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