plotters again

Brent Hilpert hilpert at
Thu Feb 22 18:13:11 CST 2007

Tony Duell wrote:
> Brent Hilpert wrote:
> > The weak point in this scenario however, is the torture of programming the
> > 9815 and problems with the tape cartridges and drive of the 9815. Those
> What's wrong with programming the 9815? I thogut it was a fairly standard
> 4-level stack RPN machine.

Let's see: 
 - awkward editing
 - the display does not show you the instruction, you have to list on the
   printer to see what you've done
 - key-sequence instructions rather than expressive language statements
 - very limited data-handling
 - limited to no structure to the language
 - etc., etc., etc., etc., etc., etc., etc., etc., etc., etc., etc., etc.

Or how about this: pretty much every lesson learned and development made in
languages and programming of the last 4 to 5 decades is missing.

I have never been fond of 'key-sequence' programmable calculators, the
'language' is not very expressive or comprehensible. In short: tortured
programming. BASIC is tortured too, but it's miles ahead of the above.

I love my HP-21, a straight-forward non-programmable 4-level-stack RPN
pocket calculator which I've had since 1976. But even back then I had no great
desire to have an HP-25 (essentially the same machine but programmable).

> > Given that the plotter uses HP-GL as the control language, I began to think
> > along the same lines as Chuck wrote about a day ago: building a simple
> > parallel interface to the plotter HP-IB port that does just the data transfer
> > (minus all the HP-IB device selection, etc. functions) to connect it up to a
> Well, the 'device selection' just means you need to be able to assert the
> ATN line so you can send a command (it's sent over the 8 data lines with
> the normal handshake sequence).

Additional complexity that's not needed in this scenario.

> 1) I don't know what the 'dedicated' 9815 interface on the 9872 plotter
> is, but there are manuals for the ploter and interface over on
>, which contain scheamtics. I think a little work
> with a 'scope or logic analyser would decipher said interface (I will bet
> the actual data sent is ascii-encoded HPGL, just as it is on the HPIB
> interface)

The 9815 interface is essentially just what Chuck did (IIUC) and I have
suggested: the 8 HPIB data lines and 3 data-handshake lines are brought across
to the controlling machine. It's HPIB minus everything but the data-transfer.

(I do have the manual with schematic. The calculator and plotter showed up at a
university surplus a few years ago and it was one of those rare instances where
it was the just about the complete package: cables, manuals, tapes, warranty card,
and enough residual evidence to show it's lineage: used by a researcher in the 
Dept. of Pathology. The pens for the plotter were missing.)

> 2) The HPIB (which I beluieve you have), GPIO (8 bit parallel) and RS232
> interfaqces for the 9815 all allw you to load or save a program over said
> interace. You could keep the 9815 and use its HPIB interface to
> communcate with some more modern machine that stored its programs, thus
> avoiding the use of the tape drive and cartridges.

I noticed this in the HPIB interface manual and was thinking about doing that,
or building a flash-memory storage device. It could have a little control
panel to select a 'file' in the flash-memory. (Probably not going to happen,
as if I don't have enough projects to work on).

However, using HPIB between another machine and the 9815 is pretty much the same
problem as using HPIB between another machine and the plotter. It would be nice
as storage for the 9815 but as far as exercising the plotter goes,
the 9815 just becomes an annoying and limiting waypoint between the
newer machine and the plotter.

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