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

retrolefty


In the end, after everything these mega1284 threads have been through, I'm still
not certain why many people are having the uploading problem. I haven't needed
the low-pass filter on RX0, and my tests earlier indicated I couldn't even reproduce
the upload problem by running the RX0 line directly through the crystal area, or
under and between the xtal pins. So ????
...........

However, I did discover a sensitivity that I forgot to mention earlier. On my mega1284
proto-test board, I am using a 6-pin header to connect the FTDI cable and FTDI Friend.
Otherwise, the RX0 pin was floating.

I found you "definitely" need to have a pullup on RX0, for when the FTDI interface is
not connected. This stands to reason, of course, as you will otherwise get noise
injected on that pin. However, unlike essentially every "other" pin on the chip, which
will be floating unless specifically terminated, noise coming in on RX0 will actually reset
the chip.

I did this test by touching each of the 1284 pins with my finger [my usual try to kill
the chip test]. Doing this had no effect for other pins, but touching the floating RX0
pin "always" reset the processor immediately. So, this is interesting....




I believe this is the same failure mode/symptom that people having trouble uploading via RX0, noise being injected via RX0 corrupting internal data bus.

Lefty

oric_dan


I read here that a 1283P owner suggested that these RX0 pin problems could be related to the PicoPower version of the chip.
Do you have a "non-P" chip to try if it shows the same behaviour (I don't have it)?

leo, so far I have been using only the 1284 "non-P" version, and have had no problems
with those. Today I ordered some of the 1284P chips, so will see how those work in a
couple of days.

leo72



I read here that a 1283P owner suggested that these RX0 pin problems could be related to the PicoPower version of the chip.
Do you have a "non-P" chip to try if it shows the same behaviour (I don't have it)?

leo, so far I have been using only the 1284 "non-P" version, and have had no problems
with those. Today I ordered some of the 1284P chips, so will see how those work in a
couple of days.

OK. I stay tuned  ;)

john1993

i can verify atmel is correct stating that uart0 is a customer layout problem. a client came to me with an m1284p board that failed to upload and we found adding a guard ring around the pin fixed it. there were several other avrs showing similar problems over the years, 90s1200 and 90s8515 being infamous examples. in every case proper layout fixed it.

oric_dan

John, do you have any idea if adding a guard ring around the next-door crystal cktry will
have a similar effect?

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