78
The 7905, 7906, 7920, and 7925 options select the disc drive model. The AUTOSIZE option selects the disc drive
model by the size of the attached disc image file. The algorithm selects the smallest-capacity drive capable of
supporting the image. This option is useful when several previously written images of various sizes are attached
sequentially.
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 option 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 7905 or 7906 Upper
and Lower Disc Protect switches or the 7920 or 7925 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 7905 and 7906 drives 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 the 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 DS<n>
Display the selected drive’s configuration
5.5.3 BOOT command
The interface supports the BOOT command to load a disc boot extension. The BOOT DS command copies the HP
12992B boot loader ROM into memory, sets the S register, and begins execution. The S register is set as follows:
1514131211109876543210
1101 DS select code unchanged head
The head number is obtained from bits 2-0 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 30 — the drive is not ready.
• JMP 2055,I — the disc read succeeded.
5.5.4 Tracing and Registers
When a debug log has been established, tracing may be configured by specifying one or more of the reporting level
options:
Option Reporting Level
RWSC
Controller read, write, status, and control commands
CMDS
Interface commands received from the CPU
CPU
Words received from and sent to the CPU
BUF
Data read from and written to the interface FIFO
SERV
Disc unit service events
IOBUS
I/O bus signals and data words received and returned
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