Put together a minimal build which runs in the EP2C5 FPGA. It does not use any external SRAM. The features are:

-- MC6800 CPU
--   Running MIKBUG from back in the day (SmithBug ACIA version)
--   25 MHz
--   4K (internal) RAM version
-- MC6850 ACIA UART
-- VDU
--   XGA 80x25 ANSI character display
--   PS/2 keyboard
-- SD Card
--   Not used
--   Included in pin list with inactive levels (in case a card is installed)
--
-- The Memory Map is:
--   $0000-$0DFF - 3.5KB SRAM (internal RAM in the EPCE15)
--   $7E00-$7FFF - 512B SRAM (internal RAM in the EPCE15)
--      $7F00-$7FFF are used as scratchpad RAM by MIKBUG
--      $7E00-$7EFF can be used by application program
--   $8018-$8019 - VDU
--   $8028-$8029 - ACIA
--     i_SerSelect (Pin_60 of the FPGA) swaps addresses of VDU and ACIA port (requires pullup in FPGA)
--     Installed (Pin_60 to Ground) uses Serial port
--   $C000-$FFFF - MIKBUG ROM (repeats 4 times from $C000-$FFFF)

 It works. It's a good baseline for starting a larger build.