How does Peggy2 drive rows with 74HC154 Decoder?
If you look into the datasheet of 74HC154, you can see that each output has an Active Low State. Also in the schematic, the leds row part use a pnp transistor (see page two). As so, they will be active if the input is low.


  This means all but one row is "on". Isn't this backwards?


Since they are PNP, the only active row is the one with Low value and the current of that row is sink through the selected column(s) in the STP16CPS05