Description

Intruduction:

Sooner or later, the Arduino starts to feel a little claustrophobic. Your sketches start running out of memory, so you need more RAM. You want to talk serial to another peripheral (like an RFID Module) AND watch the action in the Serial Monitor at the same time, so you need more UARTS. You want to use SPI and control a motor and read a few sensors, and pretty soon you’re out of pins, so you need more I/O pins. You’re logging data, and running out of 1k EEPROM fast, so a bit more EEPROM would sure be handy.

The obvious solution to this problem is an Arduino Mega 2560. Oh yeah, this thing is powerful! 54 pins! 4 UARTS! 8k RAM! You add it to your cart, and then realize it’s almost 200LE.

Now maybe you’re wondering, isn’t there anything in-between that might be a bit less cash? Indeed there is, it’s called the ATmega1284P and today I’m going to explore getting Arduino to run on it, on a breadboard.

Comparison

Here’s a quick breakdown of three chips… The 328P powers the Uno, the 2560P powers the Mega 2560, and the 1284P is the ‘Goldilocks’ chip, nestled right in the middle–EXCEPT for RAM. It has an abundance of RAM (16k!) which is important because RAM is typically the resource you run out of the quickest.

Background Reading

I’m going to build an Arduino ATmega1284P circuit on a breadboard, burn a bootloader, and upload sketches to it, all using the Arduino 1.0 IDE. This will all go better if you have done it once first with a regular ATmega328P. Doing these things on that chip is well-documented, and easy to get support on the forums if something goes wrong.

So first, read up and practice up on a 328P with help from these handy pages on the Arduino Wiki:

·      Building Arduino on a Breadboard

·      Arduino ISP Tutorial

There are three sections to the circuit show above. (Click on the image for a higher-resolution).

Power/Timing. I’m using a 16MHz crystal and 22pF caps for timing and a 0.1uF cap for power.

FTDI. I use a UGE Electronics CH340 breakout to program everything, so I’ve set this breadboard up with a connector for that mechanism.

Arduino ISP. To burn the boot loader using Arduino as ISP, six connections are needed from the Arduino. The from/to pins are indicated on the schematic.

For another view, check out this forum thread: Using the 1284p/664p (IDE, bread board and boot loaders)

Get the Software

The Arduino makes it easy to support a new ‘Hardware Platform’. The files you need are hosted on github, the Mighty 1284P Platform for Arduino.

WARNING this ONLY WORKS on Arduino 1.0. It would be possible to back-port to 0022, but seems unneeded now that 1.0 is nearing final release.

To install it…

1.    Download the ZIP File

2.    Unzip it a folder called ‘hardware’ off your sketches directory, e.g. /Users/maniacbug/Source/Arduino/hardware/mighty-1284p

3.    Restart the IDE

4.    Select Tools > Boards > Mighty 1284P

Burn a Bootloader

Once you have the Mighty 1284P platform set up, burning a bootloader is trivial. Follow the Arduino ISP instructions. You first burn the “Arduino ISP” sketch onto a regular Ardunio. Then change the “Boards” setting to the Mighty 1284P, hook up the ‘Arduino’ connections in the schematic above, choose “Tools > Programmer > Arduino as ISP” from the IDE, and then “Tools > Burn bootloader.”

To verify that it worked, move the LED to pin 1, and power cycle the breadboard. When the bootloader starts it flashes pin 1.

Upload a Sketch

Uploading a sketch is trivial now that the platform is set up and bootloader is in place. Try the ‘Blink’ example first, but change the LED pin to ‘1’ in the sketch. (Of course, move the LED back to the right pin, which is pin 2 on the MCU).

Understanding Pin Mappings

When you refer to a “pin” in the Arduino environment, e.g. “digitalWrite(13,HIGH)”, the system maps that pin onto a MCU pin. There is definitely no standard pin mapping for 1284P, many people have published their own. I chose a mapping that makes sense for the breadboard, where the digital pins start at MCU pin 1, and simply go around the chip counter-clockwise.

+—/—+
           (D 0) PB0 1|        |40 PA0 (AI 0 / D24)
           (D 1) PB1 2|        |39 PA1 (AI 1 / D25)
      INT2 (D 2) PB2 3|        |38 PA2 (AI 2 / D26)
       PWM (D 3) PB3 4|        |37 PA3 (AI 3 / D27)
    PWM/SS (D 4) PB4 5|        |36 PA4 (AI 4 / D28)
      MOSI (D 5) PB5 6|        |35 PA5 (AI 5 / D29)
  PWM/MISO (D 6) PB6 7|        |34 PA6 (AI 6 / D30)
   PWM/SCK (D 7) PB7 8|        |33 PA7 (AI 7 / D31)
                 RST 9|        |32 AREF
                VCC 10|        |31 GND
                GND 11|        |30 AVCC
              XTAL2 12|        |29 PC7 (D 23)
              XTAL1 13|        |28 PC6 (D 22)
      RX0 (D 8) PD0 14|        |27 PC5 (D 21) TDI
      TX0 (D 9) PD1 15|        |26 PC4 (D 20) TDO
RX1/INT0 (D 10) PD2 16|        |25 PC3 (D 19) TMS
TX1/INT1 (D 11) PD3 17|        |24 PC2 (D 18) TCK
     PWM (D 12) PD4 18|        |23 PC1 (D 17) SDA
     PWM (D 13) PD5 19|        |22 PC0 (D 16) SCL
     PWM (D 14) PD6 20|        |21 PD7 (D 15) PWM
                      +——–+