HP Vectra Technical Reference Manual page 293

Device busy function. This is a "hook" for multitasking systems. Currently the function just clears
the Carry flag and returns.
On Entry: AH
=
F15_DEV_BUSY (90H)
AL
=
Device Type:
o
thru 7FH
=
Device can not be shared. The operating system handling this
"hook" must serialize access to this device.
80H thru OBFH
=
Device can be shared among multiple processes. The operating
system handling this "hook" must use the ES:BX reqisters to
distinguish between calls.
OCOH thru OFFH
=
Devices of this type must wait for a fixed amount of time. This
amount of time is device dependant. Control should be returned
to the device after the fixed amount time.
List of Device Types:
OOH
=
Disc, time out required
01 H
=
Diskette, time out required
02H
=
Keyboard, no time out required
80H
=
Network, no time out required
OFDH
=
Start diskette motor, time out required
OFFH
=
Printer, time out required.
On Exit: No values returned.
Registers Altered: None.
Signals interrupt completed. This is a "hook" for multitasking systems. Currently the function
does an IRET.
On Entry: AH
=
F15_INT_COMPLETE (91 H)
AL
=
Device Type, see list of previous function.
On Exit: No registers used.
Registers Altered: None.
284 System Drivers