Trying to program Evil Mad Scientist's Peggy 2 board without their Library. The board drives an LED Matrix with:
Source 74HC154 Decoder
Sink STP16CPSO5 LED Sink Driver
What has me confused is the 74HC154 Outputs can only have one output set to Low at at time. See table below. This means all but one row is "on". Isn't this backwards? Shouldn't all outputs be low except one that is high? Selecting what row you want on, rather than selecting what row you want off. It looks more like the 74HC154 is a Sink. Thanks for any advice.
That schematic is not complete. The outputs of the 74hc154 are used to switch on 24 2STX2220 transistors. These are pnp transistors, so a low output from the 74hc154 will switch them on, while a high output will switch them off. The transistors switch current to the rows/led anodes, one at a time. The stp16d05 then sinks the current from the LED cathodes on the columns.
