HP 400 Series Servicing Manual page 61

Utility Interface (for Domain Compatible Systems)
The Domain/OS operating system uses the system clock (in conjunction with the sys-
tem-ID memories on the network controller board) to provide the proper identification
(year, month, day of the month, day of the week, hour, minute, and second) for object-
creation operations such as file creation.. Problems with object creation can indicate a
failure in the calendar device, battery, or (less frequently) a failure in reading the
memory that contains the system ID.
The Serial I/O control component of the utility interface drives four asynchronous
serial lines. Line SIO0 is the dedicated serial line for the keyboard. Lines SIO1, SIO2,
and SIO3 are RS-232, general-purpose lines. All lines are fully programmable and
support full-duplex communications. The three RS-232 SIO lines use a single 25-pin
D-sub connector on the CPU board for an external port, which limits access to a single
SIO line. An Apollo adapter cable connected to this port allows access to all three SIO
lines.
HP-HIL interface
The Hewlett-Packard Human Interface Link (HP-HIL) is the HP standard for inter-
facing HP-HIL devices (such as HP keyboards) to the system. Asynchronous serial
communications protocol enables you to select a set of input devices, connect them to
the system unit, and work with any application program.
A link controller on the CPU board controls the HP-HIL. Each HP-HIL device has an
interface for transferring information to and from the device. The HP-HIL interface
supports the following parameters:
• Up to seven devices on the link.
• Maximum distance between devices is 2.4 meters, with a total link maximum
length of 16.8 meters. These lengths do not include the 15 or 30 meter exten-
sions.
• One Ampere of +12 V dc to the link.
802.3 LAN Controller
The LAN controller has a 32-bit DIO-II interface. The controller supports either an
AUI or ThinLAN 802.3 network connection, which is jumper selectable on the CPU
board. Refer to the CPU board jumper information in Appendix A for more 802.3
LAN jumper information.
The LAN controller manages the system's interface to the IEEE standard 802.3 net-
work. The controller incorporates
• An intelligent IEEE 802.3 compatible communications controller that supports
connection of a workstation to an IEEE 802.3 network
• Support for industry standard transport media and transmission protocols
Theory of Operation 3-11