No activity on I2C Bus with PIC18F4550

jpduell · Joined: 15 Jun 2008 Posts: 2

Hello all! This is my first post and I am admittedly a novice with the PIC series of microcontrollers. I am more familiar with Altera FPGAs and Atmel Microcontrollers... I am trying to broaden my embedded systems knowledge.

As for my question(s)...
I have been trying for quite a while to get some sort of activity from my PIC's I2C interface.

Here are the various I2C init calls I have tried...
#use i2c(Master,Slow,sda=PIN_B0,scl=PIN_B1)
#use i2c(Master,Slow,sda=PIN_B0,scl=PIN_B1, force_hw)
#use i2c(Master,Slow,sda=PIN_C0,scl=PIN_C1)
#use i2c(Master,Slow,sda=PIN_D0,scl=PIN_D1)
and...
i2c_start();
i2c_write(0xAA); //just to wiggle the pins
i2c_write(0xAA); //just to wiggle the pins
i2c_write(0xAA); //just to wiggle the pins
i2c_stop();

Using an oscilloscope, I see no activity on the pins I bind to the I2C bus. I have pull up resistors on both I2C lines on my breadboard.

I have verified that the chip works by blinking some LEDs.

I am using v4.014 of the CCS C Compiler.

How do I need to set up my pins when I start a project and how would I change them after a project has been made? I believe I made B0 an input/output and B1 just an output.

What am I missing?

Thanks in advance!

-Jason

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

Do you have pull-up resistors on the SDA and SCL lines ?
You can use 2.2K to 4.7K resistors.

If you have the pull-ups, you will definitly see activity on SDA and SCL
with the following program. I tested it with vs. 4.014.

Guest · Posted: Sun Jun 15, 2008 7:03 pm

Yes... I was am using two (one for SDA and one for SCL) 10k-ohm resistors pulled up to 3.3V. The PIC is running at 3.3V as well.

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

Did you try the exact program that I posted ? If you changed it, then
post the modified program. What is your crystal frequency ?
I tested the program on a PicDem2-Plus board running at 5v.
Using the BROWNOUT fuse should not be a problem, because according
to the .LST file, the compiler defaults to BORV20 (2 volts brownout).

You said you're new to PICs. Do you have all the simple things, such
as a pullup on the MCLR pin ?

jpduell · Joined: 15 Jun 2008 Posts: 2

I just tried the program you supplied. I made no changes at first.

I did not have a 4MHz oscillator readily available, so I used a signal generator producing a 4MHz square wave as a clock source.

I still had no activity on SDA or SCL.

I have had the nReset pulled high throughout all my attempts.

I made a few changes and still no luck. I tried using the internal RC oscillator just in case the signal generator route wouldn't work.

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

I think you should check the hardware again. I've done about all I
can do.