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2-9. HP-IB Interfacing
The Hewlett-Packard Interface Bus (HP-IB) is
Hewlett-Packard's implementation of IEEE
Standard 488-1978, "Standard Digital Interface for
Programmable Instrumentation." HP-IB is a
carefully defined interface that simplifies the
integration of various instruments and computers
into systems. The interface makes it possible to
transfer messages between two or more HP-IB
compatible devices. HP-IB is a parallel bus of 16
active signal lines divided into three functional
groups according to function.
Eight signal lines, called data lines, are in the first
functional group. The data lines are used to
transmit data in coded messages. These
messages are used to program the instrument
function, to transfer measurement data, and to
coordinate instrument operation. Input and output
of all messages, in bit parallel-byte serial form, are
also transferred on the data lines. A 7-bit ASCII
code normally represents each piece of data.
Data is transferred by means of an interlocking
"handshake" technique, which permits data
transfer (asynchronously) at the rate of the
slowest active device used in that transfer. The
data byte control lines coordinate the handshaking
and form the second functional group.
The remaining five general interface management
lines (third functional group) are used to manage
the devices connected to the HP-IB. This includes
activating all connected devices at once and
clearing the interface.
The connections to the HP-IB connector on the
rear panel are shown in figure 2-4.
HP 16500A/16501A - Installation
Figure 2-4. HP-IB Interface Connector
2-10. HP-IB Address Selection
Each instrument connected to the HP-IB interface
bus requires a unique address. The address
provides a method for the system computer to
select individual instruments on the bus. The
address of the HP 16500A defaults at power-on to
decimal "07". The corresponding ASCII code is a
listen address of "'" and a talk address of "G".
2-5
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