Connecting The Interface Loop; Specifying Hp-Il Devices - HP 82479A Owner's Manual

Getting Started
2.6 CONNECTING THE INTERFACE LOOP
The HP 3421A Data Acquisition/Control Unit and other peripherals are connected to the HP-71 using
the Hewlett-Packard Interface Loop (HP-IL). To use the loop an HP 82401 A HP-IL Interface must be
installed in the HP-71. A typical loop configuration for bench measurements with the Data Acquisition
Pac consists of the HP-71, the HP 3421A, and optionally, a video interface. The peripheral devices in the
interface loop may be connected in any sequence, but all of the interface cables must form a continuous
loop. All connections are designed to ensure proper orientation.
To connect any peripheral device, first turn off the HP-71 ((fJOFF]). Then merely disconnect the loop in
any place and connect the new device at that place. All devices must be turned on for the interface to
work properly. When the HP-71 is turned on, new addresses are assigned to all devices.
2.7 SPECIFYING HP-IL DEVICES
For many HP-IL operations that you perform using the IIP-71, you'll need to specify the peripheral
device that you want to use. The HP-71 provides six ways for you to identify HP-IL devices, that 1s, six
types of device specifiers:
e Address
e Assign code
e Device word
e Device ID
eo Accessory ID
e Volume label
The first two specifiers, address and assign code, send information to a known location in the loop. These
specifiers provide fastest program execution.
The next three specifiers, device word, device 1D, and accessory ID, check each device in the loop until the
desired one is found. These specifiers provide convenient ways to identify devices. Programs that use these
specifiers aren't noticeably slower than programs that use the methods mentioned above.
The last specifier, volume label, is intended primarily for mass storage operations. Because this specifier
relates to the medium in the device, the HP-71 must read data from the medium, making this specifier
somewhat slower than the other methods, although it ensures that the proper medium is being used.
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