Designing Arduino compatible using ATmega128

I still remember some member thought about building a Arduino compatible using a 64-pin ATmega2561. Recently I obtained a ATmega128 in TQFP-64 and I want to roll an Arduino compatible out of it. Now I have a few questions:

  1. ATmega128 have a PEN# pin that have to be pulled low upon reset to enter ICSP mode. Does this mean I have to add some logic on the board to properly reset via ICSP reset pin, or should I go with the 10-pin ICSP header that have 4 GND pins tied together in the programmer, while marking the 6-pin header, like Arduino Due, as SPI only?

  2. I want to break all pins out, and that resulted in a "sub-Mega-plus" format, that is, 18x1 instead of 18x2 pins at the right of the board, and analog pins A8-12 on Mega 2560 became digital pins 38-42 and analog pins 13-15 became N/C. (I also had a sub-Mega format with the entire 36 pins on the right missing, for breaking a 44-pin PIC out into Arduino-compatible format) Is that a good idea?

  3. I chose to use CH340 as the USB to Serial adapter. Is this a good idea?

  4. What if I want to sell the design?

Suggestion please?

  1. Yeah, you gotta make sure that when you use the ISP programmer, both pins are pulled low. This can be done with a jumper. Or you could connect the PEN pin to one of the grounds on the 10pin connector :wink:

  2. The official arduino pin layout is awful, but you're shackled to that crap if you want to use $hields with it (I don't like shields - they're exorbitantly expensive, and the stackable pin header they use is almost always the crap kind that makes unreliable connections). I think most people who're advanced enough to volunteer to use an unusual chip would be fine with a more pro-mini like pinout. Preferably without the out-of-grid pins that the pro mini official pinout has, which make using it with perfboard awful.

  3. That's what I'd use. Some people prefer the FTDI one (it's a nicer part, but you don't need the functionality, and the chinese outfit that makes the CH340G doesn't pull dirty stuff like FTDI recently did (with the driver update that bricked counterfeit FTDI chips). The 16u2 that the official boards use is more expensive if you don't have Arduino's connections at Atmel, and I'm unconvinced that is in any way better.

  4. Check the terms of the license agreement on the board design software you're using (particularly if you're using a board house in the western world), and make sure you're not using any registered trademarks in your silkscreen. Also, make sure your board works well, and is free of defects that will piss your customers off.

DrAzzy:

  1. Yeah, you gotta make sure that when you use the ISP programmer, both pins are pulled low. This can be done with a jumper. Or you could connect the PEN pin to one of the grounds on the 10pin connector :wink:

  2. The official arduino pin layout is awful, but you're shackled to that crap if you want to use $hields with it (I don't like shields - they're exorbitantly expensive, and the stackable pin header they use is almost always the crap kind that makes unreliable connections). I think most people who're advanced enough to volunteer to use an unusual chip would be fine with a more pro-mini like pinout. Preferably without the out-of-grid pins that the pro mini official pinout has, which make using it with perfboard awful.

  3. That's what I'd use. Some people prefer the FTDI one (it's a nicer part, but you don't need the functionality, and the chinese outfit that makes the CH340G doesn't pull dirty stuff like FTDI recently did (with the driver update that bricked counterfeit FTDI chips). The 16u2 that the official boards use is more expensive if you don't have Arduino's connections at Atmel, and I'm unconvinced that is in any way better.

  4. Check the terms of the license agreement on the board design software you're using (particularly if you're using a board house in the western world), and make sure you're not using any registered trademarks in your silkscreen. Also, make sure your board works well, and is free of defects that will piss your customers off.

  1. I am going to use the 10-pin header and tie PEN# to one of the ground pins there. Users of 6-pin ICSP can fit a jumper on the 10-pin header to ground that pin.

  2. ATmega128 in TQFP have the same physical dimensions as ATmega2560 so the Pro Mini flavor won't work. I am stuck with the sub-Mega here.

  3. And actually CH340G is one order of magnitude cheaper than FT232 so I am using that.

  4. Do you think RivetBoard M128 a good name for such a project?