FUJITSU MHT2060BH - Manual (Page 219)

5.4 Command Protocol
C141-E203-01EN 5-145
An outline of this protocol is as follows:
1) The device receives a PIO data-out command with the Register HD FIS.
2) If an error remaining in the device prevents command execution, the device
sends the Register DH FIS with 1 set in the I bit.
3) When the device is ready to receive data, it sets 0 in the BSY bit and 1 in the
DRQ bit of the Status field of the PIO Setup FIS. At this time, the device sets
0 in the I bit of the Status field of the PIO Setup FIS for a data transfer to the
first sector, while it sets 1 in the I bit for a data transfer to any sector other
than the first sector. Then, it sends this FIS to the host. In the E_Status field,
the device sets 1 in the BSY bit and 0 in the DRQ bit.
4) The device receives the DATA FIS from the host.
5) When all data has been transferred, the device sends the Register DH FIS
(with 1 set in the I bit) to complete execution of the command. If the device
has an error, it reports the error. If any data remains to be received by the
device, this protocol is repeated starting from step 3). (The maximum data
size is 8 KB.)
Device Host
RegHD
PIOSU
DATA
RegDH
Figure 5.12 PIO data-out command protocol