ZiLOG System 8000 Hardware Reference Manual

HRM 21
Zilog
HRM 21
B.8. Seek / UNIT / CYLINDER /
The controller generates an automatic seek before disk read
and write operations. This feature can be deselected 'under
host software control. The host system can opt to defeat
the automatic seek before read/write and issue its own seek
commands. Deselection of the automatic seek facility has
the side affect of deselecting overlapped seeks in the con-
troller.
/ UNIT / Unit is written to the controller through CP1. Any
value between zero and thr~e is valid.
/ CYLINDER / The target cylinder number is written to the
controller through command ports CP3 and CP4. The low order
eight bits of the ten-bit cylinder address are issued to the
controller through CP3 and the high order two bits are
issued through CP4 bits zero and one.
B.9. Set Strobe/Offset / UNIT / SO /
The Set Strobe/Offset command is used to select a value for
either or both the data strobe timing or the head position-
ing during data read operations. Both the data strobe and
head offset are reset during disk write operations as
required by the disk drive circuitry. This command reduces
the sector read time dramatically on media that require a
strobe/offset value to recover the data. The set
strobe/offset command is useful with removable media since
it can correct small differences between head alignment
and/or data strobe times between drives. It is of question-
able merit for use with fixed media. The Strobe/Offset
value is input to the controller through the low byte of
CP1,the HEAD select register.
/ UNIT / Unit is written to the controller through CP1. Any
value between zero and three is valid.
/ SO / The Strobe/Offset value is issued to the controller
by command register CP2.
8.10. Set Write Protect / UNIT / SURFACES /
The Set Write Protect command allows each unit to be selec-
tivelywrite-protected at the controller. Write commands to
a protected surface are inhibited at the controller.
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ZiLOG System 8000 Specifications

General

Brand	ZiLOG
Model	System 8000
Category	Desktop
Language	English