A while ago lwalkera produced a few iterations of the firmware which I tested for him.
He got to one which I thought had the right settings for the printrbot and with the new G codes to set the build limits. e.g. for extended Z axis
I was hoping it would get posted on the printrbot.com site, but... <stops holding breath>
So, see attached Zipped .hex file. Insert NOT-My-Fault Legal waiver here...
Download and install FLIP with JRE (http://www.atmel.com/tools/FLIP.aspx
Connect Printrboard USB (Windows [at least my W7/64] will not find a driver)
Remove Bootloader Jumper in centre of board (for Rev A-C, for Rev D add jumper)
Windows will fail to load a driver
Use Device Manager to load drivers from Program Files(x86)\AMTEL\Flip 3.4.7\usb (took longer than I expected)
Windows recognises board
Setting/Communication/USB - Click Open
Check Blank Check box (Erase, Program, Verify should already be checked)
(a few dialogue boxes later)
Replace Boot Jumper (or remove for Rev D)
You do not have the required permissions to view the files attached to this post.