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5.4.2 Unit Options
Unit options that may be specified for individual disc drives are:
Option Action
7906H
Set the drive type to 7906H; default
7920H
Set the drive type to 7920H
7925H
Set the drive type to 7925H
BUS=<n>
Set the drive’s HP-IB address; default is the unit number
UNLOAD Set the drive’s Run/Stop switch to Stop; default when detached
LOAD Set the drive’s Run/Stop switch to Run; default when attached
PROTECT Set the drive’s Disc Protect or Read Only switch to On
UNPROTECT Set the drive’s Disc Protect or Read Only switch to Off
FORMAT Set the drive’s Format switch to Enabled
NOFORMAT Set the drive’s Format switch to Disabled; default
ENABLED
Enable the unit; default
DISABLED
Disable the unit
The 7906H, 7920H, and 7925H options select the disc drive model.
The BUS option sets the HP-IB address of the drive. Bus addresses range from 0-7, and each unit’s address must
be unique. Each unit’s bus address is initially set to its unit number.
The UNLOAD and LOAD options unload and load the drive's heads from the disc pack, setting the drive not-ready
and ready, respectively. The former provides a convenient method of setting a drive "down" without detaching the
associated disc image file.
The PROTECT option prevents writing to the disc. It is the hardware equivalent of setting the 7906H Upper and
Lower Disc Protect switches or the 7920H or 7925H Read Only switch to the On position. The UNPROTECT
option enables writing and is equivalent to setting the switches to Off. Separate protection for the upper and lower
platters of the 7906H drive is not supported.
The FORMAT option enables certain controller commands, such as Initialize, that alter the sector address fields.
Typically, this option is needed when installing an operating system. The NOFORMAT option inhibits these
commands and permits only the standard Write command, subject to the appropriate drive protection status.
Drive configuration may be displayed with the following command:
Command Action
SHOW DA<n>
Display the selected drive’s configuration
The interface supports the BOOT command to load a disc boot extension. The BOOT DA command copies the HP
12992H boot loader ROM into memory, sets the S register, and begins execution. The S register is set as follows:
1514131211109876543210
1101 DA select code unchanged 0 head
The head number is obtained from bits 1-0 of the existing S-register value when the BOOT command is executed.
Bits 5-3 of the existing S-register value are also retained and are available to the boot extension program.
Loader execution ends with one of the following instructions:
• HLT 11 — the drive aborted the transfer due to an unrecoverable error.
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