another new button related register discovered
Setting each bit of $f721 enables triggering on press as well as release of each of the corresponding latching buttons of $f723. Normally $f721 is set to zero so reading $f723 tells if a button was pressed since last being reset by setting $f728 to $01. Setting one or more bits of $f721 for example setting it to $DF would cause all buttons except the shutter button on the pv2 to report both key press and key release when reading $f723. In this case with bit 5 clear, the shutter button would only latch upon being pressed.
Setting each bit of $f721 enables triggering on press as well as release of each of the corresponding latching buttons of $f723. Normally $f721 is set to zero so reading $f723 tells if a button was pressed since last being reset by setting $f728 to $01. Setting one or more bits of $f721 for example setting it to $DF would cause all buttons except the shutter button on the pv2 to report both key press and key release when reading $f723. In this case with bit 5 clear, the shutter button would only latch upon being pressed.