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Topic: Help in programming the Atmega1284 with maniacbug-mighty-1284p. (Read 25 times) previous topic - next topic

john1993

most of the dozen or so occurences ive seen were spurious interrupts and resets due to fast signals nearby and not so much crystal issues. in the case i just mentioned and most others autorouted fill pretty much served as guard ring for the clock pins. maybe thats why this did not seems to be the cause for us. i do know there were several choices for a fix that worked and narrowed it down to resistor (no cap) right on the rx pin or ground ring. chose the latter because partlist and schematic stayed the same and much easier to refit existing boards.

oric_dan

A dozen - that's pretty serious. Can you explain the bit about "fast signals nearby" a little more.
What exactly are you talking about here? I'm not even sure what fast signals on an Arduino even
means, as I/O is pretty slow in general. The crystal oscillator is by far the fastest. Thanks.

Bajdi

A couple of months ago I had a PCB made for the ATmega1284 by Seeed. I've only been playing with electronics/Arduino for a year. So I was a bit nervous, would it work? To make it even more interesting it's powered by a LM2596 switch mode voltage regulator. I have now used the board extensively, uploaded hundreds of sketches and have not had any issues. Maybe I'm lucky? I even put the crystal and caps inside the socket. The board has an I2C logic level converter to talk to 3V3 I2C sensors and a header for a nRF24L01 wireless module. I have not tried uploading really big sketch. My biggest sketch is 30kb, anyone have an example of a really big sketch (+64kb) that I could upload?
Pic of my board: http://www.bajdi.com/wp-content/uploads/2012/12/bajduino-mega-3A.jpg

john1993


A dozen - that's pretty serious. Can you explain the bit about "fast signals nearby" a little more.
What exactly are you talking about here? I'm not even sure what fast signals on an Arduino even
means, as I/O is pretty slow in general. The crystal oscillator is by far the fastest. Thanks.


actually avr has faster io than most other chips of its type. not high frequency, high drive capability. it contributes to fast rise and fall times and avr are very high current. the xtl signal is quite slow by comparison and may actually be a sine wave if ckopt aint enabled.

but this is not what im talking about. it was external signals coming from outside the chip and not so much self-interference. specially if there were long wires from external serial. even 50ohm or 100ohm suppressed so im guessing its transmission line ringing. probably really skinny hv pulses causing clamp zeners to forward bias. that can show up in completely unrelated areas of the chip and totally unpredictable. even 100k+ worked but because im fond of avr pull-ups 1-2k would be a better choice for the series resistor there. but like i said we decided on pcb shielding instead in the case of the m1284p. btw as others noted m1284 in the same socket did not show the problem.

oric_dan

Quote
Pic of my board: http://www.bajdi.com/wp-content/uploads/2012/12/bajduino-mega-3A.jpg


Interesting, I see you're using the 1284P chip here, which is the one people have been having all
the trouble with. So, you have an smt crystal and caps underneath the chip?

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