AVR-Chat

Hi Larry,

On 4/23/06, Larry Barello <yahoo@barello.net> wrote:
> Ok, I have determined that the problem has nothing to do with the ARM / AVR
> interface.  It is the level shifting chip (PCA9512).  Well, at least it
> appears to be that: if I remove the level shifter and power everything with
> 3.3v then communications work.
>
> The symptoms are simple: On the AVR side, the peripherals never see their
> address on the bus and never assert the Ack bit.  Other than that the
> waveforms look identical (level shifter or not).  In fact, with a nice
> 500mhz DRO the waveforms look incredibly clean!
>
> I even swapped ends on the level shifter with identical results.
>
> Anyone familiar with those chips and have any clue to what is wrong???
>
> The odd thing is that if I make one of the AVR's master, it can read
> peripherals on the ARM board just fine.
>
> In examining the waveforms very carefully I determined several things:
> 1. The level shifter has very clean, slew rate limited signals.
> 2. The SCL clock is stretched when the ARM is the master
>
> Anyone have experience using the level shifting chips?

Do you have pullups on both sides of the level shifter?

What speed do you have the ARM and AVR configured for?

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