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RE: [avr-gcc-list] avrdude, ATMega128

From: Ben Mann
Subject: RE: [avr-gcc-list] avrdude, ATMega128
Date: Sun, 5 Jun 2005 21:44:44 +0800

Hi Torsten,

According to my understanding of the ATmega64 part (the only datasheet I
have readily lying around and which I suspect is sufficiently similar), the
PEN is a latched alternative to the more normal RESET programming method and
is described in the Reset Logic discussion. The SPI Serial Programming
algorithm describes this in great detail in its Power-up sequence

A quick "find" in the datasheet is very revealing...


-----Original Message-----
From: address@hidden
[mailto:address@hidden On Behalf Of Torsten
Sent: Sunday, 5 June 2005 8:45 PM
To: address@hidden
Subject: Re: [avr-gcc-list] avrdude, ATMega128


> > The supply voltages look ok.
> > PEN is connected to GND.
> This should be VCC. Not even JTAG programming works if this is GND.

i just soldered some additional capacitors to the pcb i made.  Just when i
did this, the wire that held PEN to GND fell off.

Now the program works and i see 2.5 V with the DMM on Port B (as expected)
and i see the expected pattern on port D.

Also, i soldered the additional capacitors off again and now it also works,
can erase and reprogram the device.

I see two possibilities now:

1. PEN has to be left open (i understand the data sheet differently)

2. when i soldered the SMD capacitors i had bad contact on some pads and
    i fixed that when i soldered the additional capacitors.

Any way, i wonder now why i can erase and reprogram the device even with
PEN left open.  According to the data sheet there is an internal pull-up and
PEN needs to be pulled low during reset.  On the PCB, PEN is now open and
by that pulled high during reset.  I measure 5V at PEN.

Thank you all for your hints.

Best regards,

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