>> The alternative is to come up with some GPIB to serial converter that
>> we can use to get hard copy of an instrument (an HP 3562A Dynamic
>> Signal Analyser) which has no other means of data access (Yeah, I know
>> - great project for a PIC!!).
>
>Yes, it is.  GPIB (IEEE 488) has the advantage that the bus transfers are
>all synchronous and any bus device can slow things down as needed.  It has
>8 parallel data lines and 3 handshaking lines if I remember right (It's
>been over 20 years since I worked for HP designing GPIB equipment).  The 3
>wire handshake guarantees everything is synchronous.  Once you implement
>the GPIB state machine, it should be fairly straight forward to send the
>received information to a host via RS-232.
>
>The harder part may be interpreting the information.  The plotter probably
>talks one of the many dialects of HPGL.  Figuring out which one and
>writing the HPGL interpreter sounds like the biggest chunk of work.

Yeah, I'm familiar enough with the GPIB requirements (somewhere I still have
a copy of the HP Journal with the original description of HPIB). However
what I was figuring on doing was a GPIB to RS232 converter to send the info
to a serial interface HPGL plotter, instead of a GPIB plotter, so no
translation should be required, apart from possibly needing to do some ID
things if the host instrument required it.

However further playing with the plotter suggests I may have found the base
problem. All the pens in it are rather old and dried out, which may have
been putting excessive drag on the paper, but also had gummed up the little
rubber cover that protects the tip from the environment when the pen is in
its allocated position on the pen holder. One of the rubber pieces was
missing the cover portion making the pen ooze ink everywhere and cause the
carriage to not be able to get the pen out of the holder, possibly causing
the error. I have now cleaned it all with IPA and it seems to get right
through the self test now without stopping. Least I had another plotter to
get replacement bits from :)))))

Moral - check the simple things first.

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