Here's my code:
ORG $8000 ;START OF EXTERNAL EPROM
LDX #$1000 ;POINT TO REGISTERS & ENABLE INDEXING
LDS #$FF ;INITIALIZE STACK POINTER
MAIN:
LDAA #$1
STAA $3000;ADDRESS OF LED DRIVER OUTPUT
JSR DELAY; SO WE CAN SEE IT
LDAA #$0
STAA $3000; TURN IT OFF
BRA MAIN
ORG $FFFE
DW $8000
The above snippet of code is designed to continually send a value to the LED driver's latch. In doing so, my idea was to be able to test the 74HC138 decoder as well as the 74HC373 latch. The decoder's Y3 output pulses, the LED's latch LE stays high and I am not seeing what I think I should see which is pulsing on the first LED latch output pin (Q0). I'm also wondering why I am seeing lots of activity on the PORTA output pins. Perhaps they have another task while in expanded mode?
I also have MODA and MODB pulled high to enable expanded mode.
Update: Everything works now. The activity on PORTA was the result of an incorrectly functioning CPU. After I ripped all the wires out and rewired everything, it came up!