HP-IL


The HP-IL was a short-range interconnection bus or network introduced by Hewlett-Packard in the early 1980s. It enabled many devices such as printers, plotters, displays, storage devices, test equipment, etc. to be connected to programmable calculators such as the HP-41C, HP-71B and HP-75C/D, the Series 80 and HP-110 computers, as well as generic ISA bus based PCs.

Principles

As its name implies, an HP-IL network formed a loop : each device in the loop had a pair of two-wire connections, one designated in, which received messages from the previous device in the loop; and one designated out, which delivered messages to the next device in the loop. One device on the loop is designated the controller, and manages all other devices on the loop. HP-IL cables utilize a unique two-pin connector design with polarizing D-shaped shells, and can be connected together without further adapters to extend their length.
HP-IL uses a token passing protocol for media access control: messages are passed from one device to the next until they return to the originator. When the loop is initialized, the controller sends an "Auto Address 1" message to the first device; that device takes the number in the message it receives as its own address, and then forwards the message with the address incremented to the next device. When the "Auto Address n" message finally returns to the controller, it can tell how many devices are on the loop. Up to 31 devices can be addressed using this method. Once addresses are assigned, the controller can then assign "talker" or "listener" roles to any device on the loop. By addressing each device in turn, and using the "Send Accessory ID" message, the controller can determine the role and capability of each device on the loop.
When the controller assigns listener role to a device, that device accepts and processes data received from the loop. The role of talker allows a device to originate data on the loop. Multiple devices can be assigned the role of listener at once, but the role of talker can only be assigned to a single device at a time. Data transfer between loop devices is accomplished by the controller designating a talker and one or more listeners and then sourcing a "Send Data" message.
Most devices that were designed to be used as controllers were fixed in that role, but the HP-71B was capable of assuming either controller or device mode; and with the HP 82402 Dual HP-IL Adapter, the HP-71B could even be configured with multiple loops.

Applications

Hewlett-Packard developed a range of devices to be connected to the HP-IL, mostly peripherals such as printers and storage devices for calculators. Through the 82169A HP-IL/HP-IB Interface, HP-IL controllers could be connected to instruments with an HP-IB interface, or vice versa. There were also plans to make test equipment with IL interfaces, but apart from the somewhat popular 3468A multimeter, only a few devices were introduced before HP-IL itself became obsolete.
In addition to the HP-IB interface, HP also sold RS-232 and general-purpose parallel I/O interfaces as well as a prototype kit to create custom interfaces.

HP Calculator Applications

Several HP calculators were offered with HP-IL interfaces. In the HP-75C/D it was built in, in others such as the HP-71 and HP-41, plug in interface modules were available. Popular uses for the HP-IL on the calculators included printing and cassette file storage. For ease of use, the calculators supported automatic I/O address assignment, where printer or mass storage commands are directed to the first available device of the appropriate type. Where multiple devices per type were present, a manual assignment mode could be used.

HP-IL to HP-IB interfacing

Through the 82169A interface converter, even small calculators could be used to control a number of devices on a standard HP-IB bus, an interface in wide use for test and measurement equipment. The converter can operate in either of two modes, Translator or Mailbox. Translator mode is adequate for systems where only one controller is present, while Mailbox mode applies when there are separate controllers present on both buses.
In Translator mode with an HP-IL controller, the default addressing mode is to connect the converter as the last device in the HP-IL loop, to set its own HP-IB address higher than the number of devices on the HP-IL loop, and to set the addresses of devices to be addressed on the HP-IB side must be higher than the converter's address. Deviating from this scheme requires manual control of addressing.
In Mailbox mode, the controllers on either side can place a message into the converter's buffer memory, for the other side to retrieve from that memory.

Equipment with HP-IL Interface

Controllers

  • HP 82160A HP-IL HP-41 extension module
  • HP 82973A HP-IL interface for IBM PC and compatibles with ISA bus
  • HP 82938A Interface for Series 80 desktop computers/controllers
  • HP 82401A HP-IL module for HP-71B
  • HP-75C/D
  • HP 110 aka HP Portable
  • HP 110 Plus aka HP Portable Plus
  • HP 45643A HP-IL/Parallel Interface for the HP-150
  • HP Integral PC
  • HP-3392A

    Interfaces

  • HP 82164A HP-IL/RS-232C Interface
  • HP 82165A HP-IL/GPIO Interface
  • HP 82166A HP-IL Converter
  • HP 82166C HP-IL Converter Prototyping Kit
  • HP 82169A HP-IL/HPIB Interface
  • HP 5061-3166 HP-IL/SCSI Interface
  • HP 82402 Dual HP-IL Adapter for the HP-71B

    Peripherals

  • HP 9114A/B Disc Drives
  • HP 82161A Tape Drive, with a tape, very similar but incompatible to Mini-Cassette and a capacity ≈ 130 kB
  • HP 82162A Thermal Printer
  • HP 82163A/B Video Interface
  • HP 92198A 80-Column Video Interface
  • HP 82168A, 92205M Acoustic Couplers
  • HP 82905A/B Printers
  • HP 2225B ThinkJet Printer
  • HP 7470A Graphics Plotter
  • HP 2671A/G Alphanumeric Graphics Thermal Printer

    Test instruments

  • HP 1630A/D/G and HP1631 Logic analyzers
  • HP 3421A Data Acquisition/Control Unit
  • HP 3468A/B Digital Multimeters
  • HP 5384A and HP 5385A frequency counters with option 003
  • HP 8590A spectrum analyzer with option 022
  • HP 5890 Gas Chromatograph and companion Autosampler HP 7673 have an HP-IL interface option for instrument programming and data logging using the HP 19405A Sampler/Event Control Module and the HP 3392A Gas Chromatograph Integrator as controller.
  • HP 4945A Transmission Impairment Measuring Set
  • HP 5006A Signature Analyzer

    Software

  • HP-IL Development Module
  • HP 82183A Extended I/O Module

    Third-party

  • FSI164A HP-IL/RS-232C Interface by Firmware Specialists
  • Leitz IL-41 Theodolite interface
  • CMT RAM Disc 128-512k RAM Disc; Optional RS-232
  • Ocean Scientific HP-IL A/D Interface
  • Direct Connect Modem 300 Plus Modem & Bar Code Reader
  • PAC Hardware GMBH PAC-Screen 80-col/graphics video interface with parallel printer port and mouse port
  • Interloop #111 HP-IL Repeater
  • Interloop #130 HP-IL Twinax Terminator
  • Interloop #200 HP-IL Step Motor Driver
  • Interloop #210 HP-IL IO Interface
  • Steinmetz & Brown SB10161A/2A Single/Dual 5 1/4" Disc Drive
  • Interface Instruments ADC71A Analog to Digital Converter