== Technical ==
Port decoding:
A15-A10, A8-A7 are decoded by U11.
A4,A3 from U9B.
A9 is G1, A2 = A, A5 = B, A6 = C into U10
A1,A0 are used when I/O range FBE0-FBE3.
R/W are used.
Data is used by device.
FBE0-FBE3 are decoded as 111110111110000rr
R/W not used, so read and write will access this port. Data is not important.
FBE4 is decoded as 111110111110001xx
Therefore FBE4-FBE7 access the same port.
Dobbertin HD20 is a hard disk that has an interface that appears to implement the SASI protocol (Shugart Associates System Interface).
#FBE2 Dobbertin Harddisc Select (write), Configuration (read)
#FBE3 Dobbertin Harddisc DMA, Interrupt (Used on CPC???)
#FBE4 -FBE7 Dobbertin Harddisc Reset (read or write will reset)
(Exact Port decoding: A15-A10, A8-A7 are decoded by U11. A4,A3 from U9B. A9 is G1, A2 = A, A5 = B, A6 = C into U10 A1,A0 are used when I/O range FBE0-FBE3. R/W are used. Data is used by device. FBE0-FBE3 are decoded as 111110111110000rr R/W not used, so read and write will access this port decodings to be confirmed; . Data is not important. FBE4 is decoded as 111110111110001xx Therefore FBE4-FBE7 access the GALs probably describe it)same port.
The hard drive interface is an PC-XT compatible hard disc interface.
