Re: data copy (fwd)

[Frederick Gray <fegray@berkeley.edu>]

Hi, Steve,

> Of course
> you have to get the port parameters right (parity, no. of data
> and stop bits, baud rate, etc.)  And  it is VERY important that you get 
> the cable right (normal versus "null-modem" cable configuration).  Are you
> using the cable that came with the instrument?  (it is black).
> That one worked fine when connecting a 9-pin PC serial port
> to the instrument and it was returned with the DMM.  What are you using to 
> send/receive characters?

I tried several combinations of settings (baud rate, parity, etc.) and
set them up on the computer and the DMM at the same time.  I am indeed using 
the black cable that was included in the package.  On the computer side, I'm
using minicom under Linux, and I've tried two different PCs.  The fact
that I'm able to receive characters at all (the ISOLATOR FAILED message)
suggests to me that the low-level communication is properly established.

> We used LabView 7.1 to talk to this instrument.  If you are interested,
> I can send the "virtual instrument" program that we wrote.  I think
> most of bottom-level I/O was handled by a library of "VIs" for the
> instrument that we downloaded from National Instruments "developer
> zone".

I don't know much about LabView.  I suspect this exercise would primarily
diagnose my misunderstandings of that piece of software rather than the 
hardware.

> The "isolator failed" message is a little worrysome.  Any idea
> what this means?

To quote the "theory of operation" chapter in the service manual (p. 124):

  The earth-referenced logic circuits provide all rear panel
  input/output capability.   [...] The RS-232 interface is controlled by
  U305 through U307.  [...]  Communication between the earth-referenced
  logic interface and the floating measurement logic is accomplished
  through an optically isolated bi-directional serial interface.
  Isolator U14 couples data from U305 to microprocessor U205.  Isolator
  U303 couples data from U305 to microprocessor U205.

There seems to be a typo; they probably mean to indicate a reversed flow
in one of the last two sentences.  However, I would guess that one of
these optocouplers, or something near it in the circuit, has a problem.

Thanks for your help,

-- Fred

-- Fred Gray / Visiting Postdoctoral Researcher                 --
-- Department of Physics / University of California, Berkeley   --
-- fegray@berkeley.edu / phone 510-642-2438 / fax 510-642-9811  --