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4. CONNECTING AND USING HP-IL
The Hewlett-Packard Interface Loop (HP-IL) consists of a controller
(a computer), and one or more devices (such as disc drives and printers)
connected in a series. All devices must be connected and switched on for
the loop to operate. You can have up to 31 devices in a loop.
+----------+ IN
|
Device
<------------------------------------------------<
|
|
|
2
>--------------------+
+----------+ OUT
Peripheral devices are connected to your computer (and to each other) using
HP-IL cables. A 1-meter cable is shipped with the interface card, and one
is shipped with each peripheral device.
The receptacles on the interface card indicate the direction information
travels around the loop. With the desktop PC as loop controller, instructions
and data are sent from the card through the receptacle labeled "OUT" and
are received by the card through the receptacle labeled "IN."
When only one peripheral is connected to the interface card (the card is
installed in the desktop PC), one HP-IL cable runs from the OUT receptacle
on the back of the computer to the IN receptacle on the peripheral. The
other HP-IL cable connects the OUT receptacle on the peripheral to the
IN receptacle on the computer.
If you want more than one peripheral in the loop, HP-IL cables should be
connected from the OUT receptacle on each device to the IN receptacle on the
the next device. Repeat this procedure until all peripheral devices are
connected.
The loop is completed when the OUT receptacle on the last peripheral is
connected to the IN receptacle on the computer. Note that EITHER the desktop
PC OR the Portable may be the loop controller at a given time--not both.
Instructions and data on HP-IL originate from the controller and travel to
the first peripheral, on to the second and continue around the circuit until
that information returns to the controller. If the information isn't
intended for a particular peripheral, it travels to the next peripheral
in the loop.
When the information reaches its destination, that peripheral
responds as directed and then passes on the information.
<-----------
----->
IN |
+-------v----^--------+
|
controller
|
+---------------------+
+---------------------->
| OUT
----->
|
|
-8-
OUT +----------+
Device
|
|
|
1
|
IN +----------+
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