[HH] arduino help: write protect, USB FTDI, ICSP, all connect to reset

[Drew Van Zandt]

External programming does not honor the protection bits, I don't think -
it's keeping the device from self-programming the bootloader.  RESET pin is
the one that sometimes gets +12V.

(Disclaimer: I don't do Arduino, I just read datasheets.)

http://www.atmel.com/Images/doc8271.pdf

Snippet:
28.7 Parallel Programming
28.7.1 Enter Programming Mode
The following algorithm puts the device in Parallel (High-voltage)
Programming mode:
1. Set Prog_enable pins listed in Table 28-14 on page 304 to "0000", RESET
pin to 0V and
VCC to 0V.
2. Apply 4.5 - 5.5V between VCC and GND.
Ensure that VCC reaches at least 1.8V within the next 20 μs.
3. Wait 20 - 60 μs, and apply 11.5 - 12.5V to RESET.
4. Keep the Prog_enable pins unchanged for at least 10μs after the
High-voltage has been
applied to ensure the Prog_enable Signature has been latched.
5. Wait at least 300 μs before giving any parallel programming commands.
6. Exit Programming mode by power the device down or by bringing RESET pin
to 0V.
If the rise time of the VCC is unable to fulfill the requirements listed
above, the following alternative
algorithm can be used.
1. Set Prog_enable pins listed in Table 28-14 on page 304 to "0000", RESET
pin to 0V and
VCC to 0V.
2. Apply 4.5 - 5.5V between VCC and GND.
3. Monitor VCC, and as soon as VCC reaches 0.9 - 1.1V, apply 11.5 - 12.5V
to RESET.
4. Keep the Prog_enable pins unchanged for at least 10μs after the
High-voltage has been
applied to ensure the Prog_enable Signature has been latched.
5. Wait until VCC actually reaches 4.5 -5.5V before giving any parallel
programming
commands.
6. Exit Programming mode by power the device down or by bringing RESET pin
to 0V.

*
Drew Van Zandt
Artisan's Asylum Craft Lead, Electronics & Robotics
Cam # US2010035593 (M:Liam Hopkins R: Bastian Rotgeld)
Domain Coordinator, MA-003-D.  Masquerade aVST
*



On Wed, Mar 28, 2012 at 1:10 PM, Greg London <email at greglondon.com> wrote:

>
> I wanted to incorporate an arduino into a design I'm working on.
> But I didn't want a "duino" board connected to my design,
> I wanted an atmega328 chip as part of my design.
>
> I am starting with the following schematic for a bare bones arduino:
>
>
> http://thetransistor.com/wp-content/uploads/2010/02/Minimalist-Arduino-Rev01-Schematic.pdf
>
> I wanted to keep the two connectors for ICSP and the USB FTDI
> so I can program the bootloader and also connect to it via USB
> and download arduino code.
>
> But I can't seem to figure out the reset connections between
> the two headers and the atmega328.
>
> Somewhere, and I can't find it anymore, I read that the atmega328
> has a "write protect" or some sort of bit like that on it.
> And that if this bit is set, you can't program the bootloader.
> To clear this bit, I thought I remember reading that you had to
> put 12v on the reset pin of the atmega328.
>
> Anyone know if this is correct?
>
> Anyone have a URL to a site that explains this?
> cause I can't find that website I was reading before.
>
> So, I wanted to make sure I could put 12v on the reset pin to the
> atmega328 but isolate it so I don't accidentally fry whatever
> might be connected to the USB FTDI or the ICSP headers.
>
> Yeah, I could just disconnect the header, but I was thinking I
> might solder in the USB FTDI interface because I will want
> to be able to reprogram my board.
>
> Anyway, I'm adding some 0.2v diodes to the schematic between
> the voltage regulator and the USB FTDI and the ICSP so that
> none of them accidentally fry the others with power supply
> voltages being hooked up simultaneously.
>
> I wanted to isolate the 12v to reset, but I don't understand
> how the DTR/RST from the USB FTDI works when its connected
> to reset via a cap.
>
> And I wasn't sure how the ICSP header used reset either.
>
> Does the USB FTDI reset the atmega328?
> Does the atmega328 reset the USB FTDI?
>
> How's the DTR/RST work that it's connected via a cap?
>
> Does the ICSP reset the atmega328?
> Does the atmega328 reset the ICSP?
>
> Does the ICSP put out the 12v to clear the write protect bit?
>
> If anyone has some URL's with some decent specs for what
> the USB FTDI signals do and what the ICSP signals do,
> that would be greatly appreciated.
>
> Thanks,
> Greg
>
>
>
>
>
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