RAMPS-FD schematic changes:
#3 replace C301, C302, C303 and C501 with ceramic 0805;
#4 change endstop connectors to 6x1 and 6x2 to allow key position
#9 change E-STOP connector to KK type;
#18 add 10k pulldowns on heater outputs from CPU
#19 change E-STOP buffers to HCT type to always drive FETs at 5V and remove inverting drivers on heater outputs;
#20 add 24LC256 I2C EEPROM