[time-nuts] OT: Prologix GPIB and HP3478A...The Answer!

Didier Juges didier at cox.net
Wed Nov 28 23:15:11 UTC 2007


The IOTech Micro488/P has the same basic design (microcontroller drives bus
directly) and therefore should be assumed to have the same potential
deficiency and costs about $500 today new from the factory (serial interface
only). The only limitation they show on their web site is that it can only
control up to 8 instruments, there is no mention of data rate or cable
length. I have two of them and so far they control everything I have thrown
at them. Being powered from the serial bus (they draw about 5mA), they don't
have much pull-up capability by themselves, probably very far from the
IEEE-488 spec requirements. They advertise it as being intended for laptops,
but many laptop serial ports won't provide the drive power/voltage it
requires...

http://www.iotech.com/catalog/ieee/mini_controller.html

I would like to make sure we find out where the problem is. I agree with
John that the Prologix has proven to be dependable and that the design
approach was a reasonable compromise. Measurement Computing sells a GPIB
driver chip that is in a small surface mount package, but it costs more than
the Atmel chip Abdul is using, and it's just a driver.

Didier

> -----Original Message-----
> From: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] On Behalf Of Chuck Harris
> Sent: Wednesday, November 28, 2007 1:12 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] OT: Prologix GPIB and HP3478A...The Answer!
> 
> Hi John,
> 
> I agree in part.
> 
> If it is known that certain GPIB instruments are not 
> supportable, then it is essential to have that documented 
> fact easily available to the buyer.  Thus far, the Prologix 
> website, and documentation, make no mention of any possible 
> limitations, or deficiencies.  [For instance, it clearly 
> cannot support the maximum defined GPIB system, or cable lengths.
> That should have been mentioned.]
> 
> The GPIB standard is very well defined.  There really is no 
> reason to expect that a commercially made controller wouldn't 
> be able to operate with any GPIB controlled instrument.  The 
> HP87B's controller will operate any device, and I am sure 
> that the controllers I designed as a graduate student would as well.
> 
> I would be angry, except that I already knew that the design 
> had a major short cut in it before I bought my Prologix.  If 
> you recall, I addressed that issue many months back on this forum.
> 
> I bought my Prologix controller based on the good reports 
> that all of you guys posted.  And the need to control a 
> single device, a Tektronix 7854.  It will do that, so I am satisfied.
> 
> The "Go away kid, you bother me!" approach won't win over 
> many customers.
> 
> -Chuck Harris
> 
> John Miles wrote:
> > Interesting point there.  I seem to recall quite a few 
> pullup/pulldown 
> > options in the Atmel port-configuration registers; this may 
> just be a 
> > matter of selecting a mode that looks more like the resistor 
> > configuration Chuck mentioned.
> > 
> > Personally, I think it's fine if you support only 99% of the GPIB 
> > devices out there and leave the remaining 1% to the 
> competition.  Your 
> > boards have proven compatible with an incredibly-wide array of 
> > instruments at this point.  If the 3478A problem can't be fixed in 
> > software, I think the best answer is, "Sorry, we don't support that 
> > one, here's a refund."  It certainly isn't worth adding 
> more chips (and cost) to the board IMHO.
> > 
> > -- john, KE5FX
> 
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