HP 9800 SERIES - Seek

Seek
Type:
Purpose:
Description:
HP 9895A Disc Memory Command Set A-27
Control.
The Seek command updates a unit's target address and
moves the head actuator to the new target cylinder. A seek
usually precedes a data transfer operation or a series of
consecutive
data transfers.
It is important to note that the 989SA controller is totally
dedicated to the selected drive during any drive-related
operation (e. g., the Seek command). This disallows any
overlapped seek operation between multiple drives.
The device receives 6 bytes, including the seek opcode,
the unit number, and the target cylinder, head and sector
address. Checks are made to assure that the specified drive
is available, that the entire command has been received
and that the new target address lies within the following
bounds:
HP
Single Double
IBM
Single
Cylinder address:
0<= C <= 76
H=O
0<= S <= 29
O<=C<=76
0<= H <= 1
0<= S <= 29
O<=C<=76
H=O
1<=S<=26
Head address:
Sector address:
If any of these tests fail, the status is updated and the Seek
command is aborted with a "Seek Check" indication.
The following algorithm is used to locate a logical target
track during the seek operation:
1. Determine if present logical track is the same as that
requested. If they are, then seek is complete. Other-
wise, proceed with step 2.
2.
Read current cylinder location from disc.
3.
If current address is not the location expected, then
do physical seek to cylinder O.
4. Estimate the direction and number of steps to the
target cylinder.
5.
Step actuator to target and read current head posi-
tion.
6.
If not at target cylinder address, repeat steps 3 and 4
until target found
or re-try exhausted.