ATmega USB Bit Whacker

A Complete Forth System!

These boards are from sparkfun.

Header Board for ATMega128 (sku: DEV-00035) and Breakout Board for FT232RL USB to Serial (sku: BOB-00718).

Remove the FT232RL solder jumper at SJ1 and wire VCCIO to VCC (USB is +5V).

FT232 Pin 1 TXD to ATMEGA128 pin 2.

FT232 Pin 5 RXD to ATMEGA128 pin3.

Power ATMEGA128 from USB +5V and GND.

Add a FTDI USB interface to an ATmega running amforth.

Build amforth for ATmega128. This requires AVRASM2, which comes with AVR Studio.

Here are directions for building amforth for the ATMega128 using a Mac.

You could use avra instead of AVR Studio.

Here are some examples for using amforth on the ATMega128.

The Python uploader that is distributed with amforth is described here.

I rewrote the uploader to provide error reports and to allow interacting with the ATmega from the same program before and after uploading.

My uploader : ftdi_amforth.py, an amforth shell.

I figured out the prompt match sequences by running ftdi_pexpect.py :

In [18]: s.open()

In [31]: s.write("cold\n")

In [32]: s.readline()
Out[32]: 'cold\r\n'

LOOK FOR THIS SEQUENCE:
In [33]: s.read()
Out[33]: ' '
In [34]: s.read()
Out[34]: '?'
In [35]: s.read()
Out[35]: '?'
In [36]: s.read()
Out[36]: '\x00'
In [37]: s.read()
Out[37]: ' '
END OF ERROR SEQUENCE MATCH:

In [38]: s.read()
Out[38]: '-'
In [40]: s.readline()
Out[40]: '13 10 \r\n'

NEXT PROMPT:
In [41]: s.read()
Out[41]: '>'
In [42]: s.read()
Out[42]: ' '
In [43]: s.read()
Out[43]: ''