Re: [Gumstix-users] thinking about SDA-SCL to DS1307

[Dave H. <dhy...@gm...>]

Hi Joey,

> I hope someone can help me out verify if I'm doing this right.
> I have a verdex xm4-bt connected to a console-vx. I'm thinking of
> soldering the SDA/SCL lines from the console-vx to  a DS1307 breakout board
> i have
> purchased from
> Sparkfun.com.(http://www.sparkfun.com/commerce/product_info.php?products_id=99)
> As I understand, the DS1307 runs on 5 volts, and the gumstix SDA/SCL runs at
> 3.3 volts. I'm afraid
> I might fry my gumstix again. So I'm thinking i need a pull up resistor for
> both the two lines,
> similar to the schematic I found below..
> http://www.davehylands.com/gumstix-wiki/schema_final.gif

3.3v is still considered to be a logic high by a 5v device using CMOS
technology.
What's important is that the pullups only go to 3.3v.

The inline resistor isn't really required. i2c uses open collector, so
the SDA and SCL lines are only driven to ground by either the device
or the gumstix. The pullup is what provides the logic 1.

-- 
Dave Hylands
Shuswap, BC, Canada
http://www.DaveHylands.com/