8 bit IDE interface
There is a possibility to make IDE hard disk interface much simpler. Main complication by projecting 16-bit interface was 16/8 bit data transfer between Z80 CPU and IDE hard disk.
Using only lower 8 data bits of hard disk will halving it's capacity, but by larger hard disks it should be not problem, because there is no so much Spectrum software - to fill, lets say 1 GB space. In this case interface can be made with only one chip:
IDE hard disk lines D8-D15 stay unconnected, line /SELS goes to Vcc (+5V), and this is all with hardware.
TUP - any low power PNP silicon transistor. E.g. BC327, BC212.
Position of pins on connectors you may find on 16 bit interface scheme .
I/O addresses for this solution:
Data register : #2B
Parameter reg.: #2F
Sector count r.: #6B
Start sector r.: #6F
Cylinder low : #AB
Cylinder high : #AF
Head reg. : #EB
Example routines for multiple sector read/write for this interface are in : 8-bit programming reference .