Power-On Self Test - HP Vectra Technical Reference Manual

10.3.1 Shut Down Status Byte
The shut down status byte is used by the system to determine what action should be taken on
reset. Table 10.1 shows how the shut down status byte is interpreted. Note that any value that
does not indicate a return from protected mode is interpreted by the system as a reset, and will
cause the reset process to invoke POST.
Table 10.1
Shut Down Status Byte
Value
00-04H
OSH
06-07H
08H
09H
OAH
OBH-FFH
Definition
Perform power-on reset sequence.
Flush keyboard and jump via double word stored at 0040:0067H.
Perform power-on reset sequence.
Retu rn from test of extended memory.
Return from INT 15H block move function.
Jump via double word stored at 0040:0067H.
Perform power-on reset sequence.
The values 08H and 09H are used internally by the ROM BIOS. If the return from protected mode
process detects either of these values, it will branch to their respective routines. Values
OSH
and
OAH
should be used by all other programs returning from protected mode.
10.4 Power-On Self Test (POSn
Each time the system is powered-on, or a reset is performed, the POST process is executed. The
purpose of the POST process is to verify the basic functionality of the system components and to
initialize certain system parameters. The POST process performs the following tasks:
System Processes 31 5