HP Key Notes January-February 1982 Vol. 6 No. 1 - HP-IL Introduction

Copyright 1982 by Hewlett-Packard Company. Reproduced with permission.

HP-IL Introduction

On December 21, 1981, the Hewlett-Packard Interface Loop concept became a reality. This date marked the beginning of a new era in low-cost systems for electronic data transfer and electronic control.

Now, your HP-41 hand-held computer can easily communicate with, and control, any Hewlett-Packard Interface Loop (HP-IL) peripheral. Present HP-IL peripherals include a printer, a digital cassette drive, a converter, and a digital multimeter. But that's not all. A video interface has been announced but will not be available until later this year. Also, with the new HP82938A Series 80 HP-IL Interface Card, your HP Series 80 Personal Computer can interact with your HP-41 through HP-IL, and it can act as a controller of the HP-IL loop. And, with the addition of the new HP82182A Time Module, your HP-41 becomes a care-free, time-based controller. Ah, but this is jumping ahead; let's discuss the fundamentals.

The HP-IL concept revolves around a two-wire cable that can connect as many as 30 HP-IL devices in a closed series loop. HP-IL is a "master-slave" interface, meaning that one active controller regulates the information flow between all of the devices in the loop. Data and commands move around the loop in one direction.

The reason we use such terms as "the controller" and "a device" is because HP-IL is a general-purpose interface. The elements of the system that you choose to use will be tailored specifically to your application. This is the flexability of the HP-IL concept.

At the core of this new concept is the new HP82160A HP-IL Module. This module fits into any of the four HP-41 ports, and it expands the HP-41 with a powerful set of functions for interaction with the devices in the loop. Now, printers, mass-storage devices, and a variety of instruments can be controlled by the HP-41 through one port!


The new HP82161A Digital Cassette Drive is an HP-IL mass-storage device. Each of the digital mini-cassettes driven by this device can store up to 131,072 bytes of data, programs, status information, and directory in files that you name. Just think: 131,000 bytes is over 50 times the full RAM capacity of the HP-41CV! In fact, we have stored on just 3/4 of one mini-cassette, all of the prorams in every HP-41 "Solutions" book! This is why we call it mass storage. Also, the HP82161A Digital Cassette Drive is fast, with an average file access time of 13 seconds, and a 30- second maximum rewind time. Yet, accessing a program file is easy. With the Digital Cassette Drive in the loop, simply place the name of the file in the ALPHA register, key in [XEQ] "READP", and the program is available in the RAM of you HP-41 within seconds. Other files are accessed (and recorded) just as easily by executing different HP-IL commands.


The new HP82162A Thermal Printer/Plotter is an HP-IL compatible device that is similar in appearance and function to the HP82143A Thermal Printer/Plotter. In addition to all of the convenient features of the HP82143A Thermal Printer/Plotter such as double- and single-wide printing, right and left justifying, 128 standard characters, and special character building, the new HP-IL printer has a FORMAT statement that allows you to automatically center words on the page and to easily right- and left-justify two columns. Plus, the new HP82162A Thermal Printer/ Plotter has a 101-element buffer, and a STANDBY position of the on-off switch helps conserve battery power.


With HP-IL, your HP-41 can control and take data readings from, the new HP3468A Digital Multimeter. Or, if you have a considerable knowledge of electronics and interfacing techniques, you can use the new HP82166A HP-IL Converter to connect your own 8 or 16 bit-parallel device into the HP-IL system.

A general application of such an HP-IL system would use the new HP82182 Time Module, which is discussed in the following article, to "wake up" the HP-41 in the middle of the night, while you are at home sleeping. Automatically, then, the HP-41 would begin to execute a control program. HP-IL allows you to program the HP-41 to power-up devices in the loop, take readings from instruments, make data listings, read subprograms from mass storage devices, and interact with other devices in the loop as prescribed by the programs. The extensive programming capabilities of the HP-41 allow it to make critical decisions based on the data received from the instruments in the loop and interact with other devices in the loop, accordingly. Then, with its job complete, the HP-41 can power-down the devices in the loop, including itself. When you arrive at work in the morning, after a good night's rest, a printer listing awaits you, documenting the events of the night as monitored by the HP-41!


At this point, you have read the introduction to an entirely new concept in electronic commuication and control that represents a major technological breakthrough. This is a good point to sit back, relax, and think about the implications of the HP-IL concept. Just think: now, with the HP products that were announced on December 1, 1981, thousands of electronic control applications can be tackled by portable, affordable, devices.

And, this is only the beginning. Hewlett-Packard is committed to continuing its quality support of HP-IL. The devices that are compatible with the HP-41 as a mainframe controller will be compatible with future hand-held computers and personal computers with input/output capabilities. Many HP divisions - in the instrument and computer areas - will be introducing HP-IL devices.

We have enough space to give you only a small taste of the broad capabilities of HP-IL. See your local HP Dealer for a look at the new HP-IL system, and see if it will meet your challenge; we'll bet it can - and does!

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