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

[Chuck Harris]

Didier Juges wrote:
> Yet it works fine with mine, even with or without a number of other
> instruments on the bus, powered or not. I have not come across that problem
> with either the Prologix of the IOTech Micro488/P which also uses a
> microcontroller (Motorola 68HC705C4) to directly drive the bus (no GPIB
> driver chip).

Ok, that pretty well rounds out the picture.  The 3478A uses the
75ALS160 and 161 bus drivers.  Both are designed to be either tristate
or pullup drivers depending on the signal on a single pin.  I will have
to put a scope on mine and see what it is being told to do.

Driver chips do fail... all too often, actually.

> 
> There has to be something else wrong, maybe the 3478 is partially defective
> and requires too much drive, or is lacking the right pullup. The fact that
> it works with the HP 85 indicates that it is not completely dead, but there
> could be something wrong with it that makes it incompatible with the
> Prologix.
> 
> I agree that it is always best to follow the standard, but in this case, I
> doubt it is the root cause of the problem.
> 
> My HP 3478A has serial number 2619A36441, switch 6 (Power ON SRQ) is down
> (0), switch 7 (not sure what it does) is up (1) and switch 8 (50/60 Hz) is
> down (0)

Switch 2 (what you call 7) is said by HP to be not used.  I have tried
mine in both positions, and see no change.

-Chuck Harris