Quick notes on using sd2iec with an mbed LPC1768:
- if in any doubt, wait until someone has designed a nice PCB for this
- this information can become obsolete faster than you expect, so
  don't complain if you need to rewire your device
- an XPresso LPC1768 should also work, but I haven't tested that
- UART 0 is the debug serial port (USB-connected on mbed)
- an external 24C02 or similiar EEPROM is required for the
  configuration settings - steal one from an old DIMM ;)
- an external 3.3V regulator may or may not be required
  (I'm using one, but VOUT of the mbed may be sufficient)
- SD card interface:
  - p11  DI
  - p12  DO
  - p13  CLK
  - p14  SD card CS
  - p17  card detect switch (grounded if card inserted)
  - p18  write protect switch (grounded if write protection disabled)
- I2C interface to the EEPROM (and display - untested!)
  - p9   SDA
  - p10  SCL
  - use external 4k7 pullups to 3.3V!
- address selection
  - p21  8/9
  - p22  8/10
- buttons
  - p23  Next
  - p24  Previous
- serial bus
  - inputs connected via a 74HCT14 (LS is ok too, HC is NOT)
  - outputs connected via a 74HCT06 (LS is ok too, HC is NOT)
  - inputs:
    - p15 ATN
    - p30 Clock
    - p29 Data
    - p16 SRQ
  - outputs:
    - p6 ATN
    - p8 Clock
    - p7 Data
    - p5 SRQ
