Interface Functions - HP 9000 Series 300 Tutorials Manual

Interface Functions
A usable interface must fill the following system requirements:
• Electrical Compatibility: The interface must convert electrical signal
voltages, currents, frequencies, and timing from the computer to a
form that is useful to the peripheral device, and vice-versa (unless no
conversions are necessary). It must also provide any special protection
that might be necessary to protect circuitry within the computer or
peripheral from damage due to external effects related to the interface
cable or power source.
• Mechanical Compatibility: The interface must be mechanically
structured so that it is readily connected to both the computer and the
peripheral device. This is usually accomplished by means of an interface
cable that has appropriate connectors on each end.
• Data Compatibility. Just as two people must speak a common language
before they can communicate well, the computer and peripheral must
use compatible forms of communication. While in most cases, the
computer operating system and the programmer are responsible for
general data format, communication protocols such as those used
in data communication networks and HP -IB interconnections are
usually managed by the interface card, based upon various signals and
commands from the computer and the peripheral device.
• Timing Compatibility. Peripheral devices within a given system rarely
have identical data transfer rates and data transfer timing requirements.
They also rarely match the timing and transfer rates in the computer or
other devices in the system. For this reason, one of the most important
functions of the interface is to manage and coordinate the interaction
between the computer and the interface as well as timing between the
interface and peripheral devices by using special timing signals that
are inserted into the data being transferred (most common in data
communication interfaces) or carried on separate control signal lines
(typical for HP-IB and GPIO interfaces). These timing signals are used
to coordinate when a transfer begins and at what rate the information
is handled.
• Processor Overhead Reduction: Another important function of the
interface card is to relieve the computer of low-level tasks, such as
1-6 Interfacing Concepts