Starting with pc_fast_blinker_sub
step 1 adding rom
step 2 reading back the values.
step 3 changing rom to ram
step 4 wrting to ram
step 5 reading back the values
chg'ed name from pc_fast_blinker_sub to ram_rd
using 3 files from windows8_XulA2-LX9/pc_fast_blinker_sub
Common.vhd, HostIo.vhd, and SyncToClk
adding rom_rd.vhd
see signal_generation.doc for details