Is the charge pump circuit schematic available anywhere ?   I saw it once, several months back on the artsoft site, but I can not find it now when I need it.

Thanks,
Joel

Here you go!

Awsome, thanks for the FAST replay....

And do I need one?

Depends what system you've got and how it's set up but in my opinion anything that is connected to the parallel port of a PC needs one or something similar. If you can remember the days when a printer was actually connected to these ports everytime you switched the computer on the printer would burst into life for a few seconds then go quiet again. This was due to port testing being done as the PC got ready to do work. So if you now connect a bit of drive circuitry and a motor to the same port then the likely hood is it will also burst in to life in an un predictable manner every reboot of the PC. The other big problem is PC crashes, during this time everything or nothing maybe being whizzed out the printer port and obviously again the motors may act in a dangerously unpredictable manner. The gents above have described how the charge pump works quite well so I'd just add this. There is a part of the mach software that ensures there is a 12.5KHz signal on a pin of the parallel port whilst it has control of the PC and the port the chances of this 12.5KHz signal appearing during reboot or PC crash is v v unlikely so it is a safe way of ensuring your motors only receive a signal to move when Mach has control.