HP Apollo 9000 400dl, Servicing Manual, Page: 105 / 296

Fault Isolation 4-35
The following algorithm is used to determine the output device:
1. If there is a remote card, choose the one with the lowest select code.
2. If there is an internal bit mapped display controller, choose it as console.
3. If there is a bit mapped display controller in DIO-II space, choose the one with
the lowest select code. If not go the next step.
4. Use dummy display drivers.
Only one output device at a time is used as the console output device; however, the
Boot ROM initializes and clears any bit mapped video/graphics board that it finds,
even if that board is not chosen as the console device. Note that if a device fails self-
test then, the device is considered not present. The Boot ROM always tests a device
before choosing it as the console output device.
Input Devices
Common input devices include the HP 46021A Keyboard or a terminal connected to
the RS-232 interface. Keyboards may be directly connected to the HP-HIL interface
port, or to one or two graphics display controllers connected to a local graphics bus
interface board. HP-HIL interfaces in graphics display controllers are considered an
external interface.
Note that if an internal HP-HIL interface and a remote terminal are both present in a
system, they are both enabled. Similarly, if an external HP-HIL interface and a remote
console are both present in a system, they are both enabled, provided no internal key-
board is present. An external interface is never enabled when an internal interface is
present.
When more than one external keyboard is present, the one with the lowest select code
is enabled. If several HP 98735 Graphics Display Controllers exist on a system, then
you must ensure that the external keyboard associated with the display controller at the
address 560000
16
has the lowest select code of all the external keyboards in the system.
This must be done to ensure that the keyboard associated with the first display control-
ler is not input console while the second display controller is output console. The Boot
ROM does not attempt to verify the display/keyboard relationship.
If a keyboard controller or a remote RS-232 card fails, then it is considered by the al-
gorithm to be not present. For example, if an internal keyboard fails self-test, a
Keyboard Failed
message is displayed; however, the input device search algorithm
goes ahead and looks for an external keyboard. The Boot ROM always tests a device
before choosing it as the console input device.