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A-8 HP 9895A Disc Memory Command Set
Command Execution Checks
In addition to the above holdoffs, the controller will verify other conditions before a particu-
lar operation is permitted to execute.
1. Correct number of command bytes.
Obviously, the correct command syntax must be received, or else an I/O program
error is defined by the controller.
2. DSJ
=
1 and status 1
<>
I/O program error
DSJ
=
1 and status 1
< >
illegal opcode
The above condition exists when the most recent command terminated with an error.
The following commands are disabled when this condition exists until the host system
requests status and hence is aware of the status of that last operation:
a. Read commands,
b. Write commands,
c. Door lock/unlock.
3. Disc format.
Most commands that operate on the disc will verify that the format is either HP or IBM.
If an unknown disc is in the requested drive, these operations will abort with a status 2
error. The commands are:
a. Seek,
b. Read commands,
c. Write commands,
d. Initialize command.
4. Obviously, the disc must not be write protected when any command that needs to
write information on the disc is given. The commands that make this check are:
a. Write commands,
b. Initialize command,
c. Format command.
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