AVR-Chat

kernels_nz wrote:

> Hi Guys,
> 
> I have a very weird problem with my Mega16 (DIP40) running a 16MHz
> crystal (22pF loading caps).
> 
> Im trying to read incoming data on PIND.0 very rapidly (approx 150kHz)
> and the chip just doesnt seem to work correctly. It works perfectly if
> I use either PIND.7 or PIND.2 (the only other 2 pins I tried). But as
> soon as I swap it back to using PIND.0 it stops working again.
> 
> Ive also assertained that the program works fine if I use an internal
> 8MHz oscillator instead of 16MHz crystal. So I think it might have
> something to do with the fact that PIND.0 is right next to a crystal
> pin. Could noise from the crystal pin be coupling to the data input
> and corrupting the data stream somehow ? could this be happening
> inside the Mega16 ? If so it is unfortunate that Atmel have placed the
>  RXD pin of the UART right next to the crystal pins.
> 
> Unfortunately I really do need to use a 16MHz crystal also, so merely
> ignoring the problem and using a slower oscillator will not work !
> 
> WOULD APPRECIATE ANY SUGGESTIONS !!!
> 

Please post your fuse settings for the osc / clk setup, also have you got all 
the VCC and Gnd pins connected ?

22pf is a little low for most HC49 crystals, more common is 27 or 33pf (30pf 
is the ideal)

-- 
Regards,

Kat.
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