remarks
=======

see introduction and nice documentation:

http://www.raspberrypi.org/forum/educational-applications/gertboard
http://raspberrycenter.de/tags/gertboard
https://projects.drogon.net/raspberry-pi/gertboard/


differences to the original Gertboard:
* no patchfield
* nearly all discrete parts (R, C) as SMD on the bottom side
* low frequency (32.768 kHz) clock oscillator, so the internal oscillator can calibrated
* no connection betwee Aref and AVcc; use ADMUX (REFS1, REFS0) if you need it
* rotate the voltake regulator and the motor driver to easy mount heat sinks
* reduce maximum current for motor driver from 4 A to 2.5 A to avoid overload of thin PCB traces
* reduce description on PCB to fit on 100mm x 80mm size (eagle light)

remaks on assembly:
* check the fuse holder (pins across) is avalible
* for buffers suggest 74AC244, if you use 74HC244 the inputs will float
* for buffers ACT and HCT not suitable, because 5V supply voltage
* you can use 74LVX244 if you adapt the layout to the different package

remakrs on ATmega/Arduino
* you can choose between GPIO/ISP and RX/TX-bootloader zu prorgam the ATmega

* the bootloader was enhanced with a calibration function;
  OSCCAL is so midified that the internal RC-oscillator will swing on the freqency set by F_CPU
  serial protocal works up to 115200 bps

* to use the bootloader you need an initial setup:
  > make bertboard168_isp

  look here to see the necessary connections between raspberry pi and ATmega:
  https://projects.drogon.net/raspberry-pi/gertboard/initial-setup-of-the-atmega/

* you can use the upload feature of the arduino-IDE after modifications on boards.txt and programmers.txt

* the upload via bootloader works only, when its active.
  You can connect button B1 with AVR-ISP Pin5 (/Reset).
  When in arduino-IDE the program size appear, after compile, release fast the button,
  to activate the bootloader. Maybe you need some practice for the right moment.

advantage vs. disadvantage:
+ calibrated clock and stable uart connection
+ more free IOs: PB3, PB4 and PB5 (MOSI, MISO and SCK)
- 2 kByte less space for own programs on ATmega
- no support for auto-reset at the moment
