I2C clock frequency?

[Dave]

Qacer, When it does the compile it uses the "OSC=" directive to calculate the data output rate. Make sure you are declaring the OSC=20 if you are using a 20Mhz. oscillator.

Dave Purola,
N8NTA

[Qacer]

Thanks, Dave!

Coincidentally, I'm trying to figure out the oscillators used in the PIC12F675. I have not quite figured out that part, yet.

Do I need to define OSC every time I use the I2C routine?

Thanks again!

[mister_e]

The internal oscillator of the 12F675 run at 4MHZ. if you want to run @29MHZ you must use an external Crystal or a ceramic resonator.

The DEFINE OSC must be place somewhere on the top of your code and you don't need to write it every time.

[Qacer]

Thanks!

Would serial communication with a 400KHz I2C device still work if my PIC oscillator setting is at 4MHz?

[mister_e]

of course yes, if not we should all use 400KHZ or less as oscillator. PBP generate the right clock frequency for you. Look in the manual in the I2CREAD/I2CWRITE

[Qacer]

By the way, I wanted to use the internal 4MHz oscillator. From what I heard, that the frequency of oscillation might not be as stable. Would I2C communications still work if I go this route?

[mister_e]

Unstable yes and no. At least, i would never trust too much a serial communication RS232 or else running with any internal or ceramic resonator. Worst if the final product maybe use in various ambient temperature.

For I2C... i never got issue even by running internal OSC... well as now