|Re: Hp 71B|
Message #11 Posted by Garth Wilson on 4 Feb 2006, 2:44 p.m.,
in response to message #6 by Vassilis Prevelakis
This interface can fit within the HP-IL controller cavity and will be far more useful than the (obsolete) HP-IL interface.
HPIL is obsolete only in that it is out of production. It's good for only the medium speed of about 5,000 bytes per second plus overhead (even USB 2.0 may not be able to go any faster with an HP71 though), but HPIL has a lot of benefits over other interfaces. It allowed simultaneous interfacing to anywhere from one to hundreds of other devices with a single pair of small, inexpensive connectors and no external hubs, was plug-n-play, did auto-addressing and error-checking, every device knew what it was and what it could do, it supported hot-swapping and interrupts, had 1,000-volt isolation between any two adjacently connected devices (by the pulse transformers), and allowed passing control from one controller to another if you had two or more controllers on the loop. There were interface converters to the other major interface types-- parallel, RS-232, and HPIB (IEEE-488). Being less expensive and more intelligent than HPIB, it should have become an industry standard, but unfortunately HP marketing killed it like they did the 71. The 71 was made for technical professionals; but not one in ten of them knew it existed; and of those who did know, not one in ten had any idea how much power it had.
USB is the common interface now. It's faster, but it has the huge disadvantage that you need an additional port for each thing you want to connect. (That's a problem when you have limited space for connectors, like on the 71.) Distance is more limited too. Again there are converters to the different interface types though, so a USB port can be connected to RS-232, HPIB, and hubs to more USB ports.
The only other interface I can think of right now that had the isolation like HPIL is MIDI, which uses optoisolators instead of pulse transformers. The optoisolators made it less suitable for low-power hand-held operation, the connectors are bigger, and its fixed speed is slower, at 31.25kbps. It did allow daisy-chaining, but there was no error-checking.