Can be used as a replacement of the original LEGO IR serial tower with programs and platforms such as

• WebPBrick: web-based NQC IDE (see also: github.com/maehw/WebPBrick/)
• Bricx Command Center (BricxCC): 32-bit Windows IDE
• firmdl3 command line download tool
• probably other software

to load user programs and firmware on the yellow LEGO Mindstorms RCX programmable brick.

Pin Assignment Table for the ATtiny13A:

Find the productive firmware in folder ./firmware.

To build, run:

avr-gcc -g -Wall -Os -mmcu=attiny13 -o main.elf main.c

Want to check if it will it fit into the internal flash?

avr-size main.elf
   text	   data	    bss	    dec	    hex	filename
    776	      0	      7	    783	    30f	main.elf

Make sure to burn the fuses so that

• the calibrated internal 9.6 MHz oscillator is selected
• clock pre-scaler set to 1 (device is shipped with CKDIV8 programmed).

Reading fuses with avrdude (and in this case an ehajo-isp in-system programmer):

avrdude -c ehajo-isp -p t13a -U hfuse:r:-:h -U lfuse:r:-:h 

Flash the firmware:

avrdude -c ehajo-isp -p t13a -U flash:w:main.elf:e

LEGO® is a trademark of the LEGO Group of companies which does not sponsor, authorize or endorse this project.