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Topic: Regression between uno and uno R2 VALIDATED. HARDWARE PROBLEM CONFIRMED (Read 27 times) previous topic - next topic

robert rozee

#40
Jun 22, 2011, 06:14 pm Last Edit: Jun 22, 2011, 06:17 pm by robert rozee Reason: 1

[...]
Maybe not so unpredictable. Isn't a higher then Vcc voltage to the reset pin the method that puts the chip into it's high voltage programming mode? As I understand it the reset pin does not have an internal positive clamping diode to Vcc (unlike the normal I/O pins, just because of the higher then Vcc on reset method to enter HV programming mode.
[...]
Lefty


good point! i wonder if HV programming mode looks at the non-PWM digital pins, and all-zeros represents a no-operation/exit, while anything else (ie, a 4k7 pullup present) initiates something else?

there are indeed more complicated solutions than a simple diode-fix, that would still allow for the HV  programming, though none that can be retrofitted easily to an existing board. the 'correct' solution would be to replace the 0.1uF capacitor and 1k pulldown with a monostable.

as an aside, that 1k pulldown wastes 5mA of current drain.

foubarre

Quote
Would this then prevent the arduino board from being able to be programmed via the 'high voltage' method? Granted that would represent a very small population of users, however I've seen at least one shield based high voltage programmer avalible for sale. It allows those that have managed to 'brick' their processor by errors in fuse settings, i.e. change reset pin to be a I/O pin, etc.

If it does, it's easy for new design to add two via around the diode to shunt it easily using a basic wire, or even add an open pad to be shunt with solder.

By the way, some diods seem to anihilate the reset for programming, so choosing the right one matters a bit.

retrolefty

#42
Jun 22, 2011, 06:42 pm Last Edit: Jun 22, 2011, 06:44 pm by retrolefty Reason: 1
Quote
If it does, it's easy for new design to add two via around the diode to shunt it easily using a basic wire, or even add an open pad to be shunt with solder.


But wouldn't that also shunt out the reset's pull-up resistor to Vcc, which would then cause direct connection from Vcc to the high voltage pulse/level used in HV parallel programming mode?

Lefty

robert rozee

#43
Jun 22, 2011, 07:02 pm Last Edit: Jun 22, 2011, 07:03 pm by robert rozee Reason: 1

Quote
If it does, it's easy for new design to add two via around the diode to shunt it easily using a basic wire, or even add an open pad to be shunt with solder.


But wouldn't that also shunt out the reset's pull-up resistor to Vcc, which would then cause direct connection from Vcc to the high voltage pulse/level used in HV parallel programming mode?

Lefty


i think he meant to say "in series with", with the jumper shorted by default.

re: not all diodes working - it will need to be a small-signal one, such as a 1N914, 1N4148, etc. a power diode such as a 1N4002 will potentially not clamp quick enough, allowing the HV pulse to still get through. other power diodes may, as you've seen, swamp a valid reset pulse.

westfw

I'd be happier if I understood how the changes in the schematic (a pull-down resistor on the other side of autoreset cap) end up causing/allowing this spike...  (I also don't understand the motivation for ADDING that resistor in the first place,
so ...  I dunno.)

PD7 is involved in high-voltage parallel programming; it's (renamed PAGEL) supposed to be tied to 0 to enter HV programming mode (which is somewhat backward from the observed behavior.  But it certainly seems reasonable that HV excursions on RESET could trigger SOMETHING.)

None of the HV programming shields I've seen involve using that programming while the chip is mounted IN the arduino; they all move it to a separate socket.  HCV programming involves 9+ pins, including the crystal pins, so it's not really meant to work with the AVR "in circuit."

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