Testing an assembly routine for rendering text, as I need a significant performance boost. The C text render routine uses too many cycles. Fast blank pixel switching stopped working. It was only switching to contrast-reduction mode, pixels were not appearing. It was as if the voltage level on the FB pin was not high enough to switch to pixels although according to my scope the voltage levels were correct. This appears to have happened when I connected the ground for the FB DAC. Previously I did not have this connected.
After I removed it it started working again. Relieved to see it work once more although in fact it is supposed to have ground connected.
I think the reason it needs GND disconnected is because in contrast-reduction mode, one of the 2 FB pins is at level 0 (i.e. ground) so it is acting as a second ground. That is why the DAC still works without its GND connection. This behaviour of digital pins at level 0 means I have probably miscalculated all the resistors in the other DACs, although colours seem OK.
Weka OSD 