LEDG0	- disk (SD) activity (for real!)
  LEDG1	- disk selected
  LEDG2	- Ethernet selected
  LEDG3	- CAS: relay    (OUT 58,32)
  LEDG4	- CAS: data out (OUT 58,64)
  LEDG5	- turbo 3 (25 MHz)
  LEDG6	- turbo 2 (12, 25 MHz)
  LEDG7	- turbo 1 (6, 12, 25 MHz)

  LEDR9-0 just show the status of SW9-0

  KEY0	- Reveal text
  KEY1	- Video mode test
  KEY2	- CPU reset
  KEY3	- Turbo mode
  
  SW0	- SD card inserted
  SW1	- SD card write protect
  SW2	- physical serial port is V.24 not printer
  SW3	- suppress blue (use for green or amber screen)
  SW4	- suppress red (use for green screen)
  SW5	- monitor calibration test pattern
  SW6	- suppress blink
  SW7	- reverse video
  SW8	- no turbo (3 MHz default)
  SW9	- 40 column default