no not quite... The charge pump is a small circuit designed by Mariss Freimanis of Geckodrive which has an input. This input is connected to an output on the printer port which has been assigned as the Charge Pump signal.
When Mach is running and not in an error state this output has a 12.5kHz pulse appearing on it.
The circuit mentioned above, monitors this signal and if it dissapears for any reason opens a relay, this relays contacts would normally be part of the external E-stop chain. So if it opens your drives etc could be disabled.
Wayne...