[time-nuts] A Prologix GPIB-USB hint

Poul-Henning Kamp phk at phk.freebsd.dk
Sat Jun 9 14:32:06 UTC 2007


I spent the better part of an afternoon trying to figure this bit out,
so to save somebody else the time:

Some GPIB instruments will complain if addressed to talk when they
have not been asked about anything.  The HP6626A Power Supply is
my present instance.

The Prologix GPIB-USB has the "++auto" command which controls if
it should automatically go into listen after a talk, the description
on the manual page is:

	Enable (1) or disable (0) "listen-after-talk" feature

Based on that description, one would, or at least I would, expect
the behaviour to be that nothing happens until the next write,
so that this would work:

	++auto 0
				idle bus
	write something
				device= listen
				send data
				idle bus
	++auto 1
				idle bus
	write something
				device= listen
				send data
				device= talk
	read something


But that is not the case.  "++auto 1" puts the device in talk
mode immediately, so the sequence needs to be:


	++auto 0
				idle bus
	write something
				device= listen
				send data
				idle bus
	write something
				device= listen
				send data
				idle bus
	++auto 1
				device= talk
	read something

You've been warned :-)

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.




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