[u3b.tech] 3B2 - HP7750A Woes

tim@attdso.att.com (Tim J Ihde) (01/19/89)

We're having a peculiar problem with some HP-7550A plotters connected
to our 3B2/400 (we actually have three of these plotters; each manifests
the problem).  From what I can tell, it appears that the plotter is
unable to XOFF the computer when its buffer fills up.

The error manifests itself mainly when plotting a complex bar chart that
has some long filled bars in it.  If the baud rate is high, say around
2400 - 4800, we get "Buffer Overrun" almost as soon as the bars are begun.
At lower speeds, down to 300 baud, it plots longer but still gets the error
eventually.

The really peculiar thing, which I still don't really believe, is that
it seems to work much better with paper than with transparencies.  How
the plotter handles transparencies differently, and how it knows they are
there instead of paper in the first place, I don't understand.  This seems
pretty consistent, though.

Anybody have any ideas?

Our plotter settings (from the panel) are:
	Enhanced Serial
	Handshaking = XON/XOFF Direct
	Bypass = Off
	Data Flow = Remote Standalone
	Duplex = half
	Parity = 8 Bits, none
	Baud = 600 (works almost always for paper, occasionally for transp.)

The lp interface script we are using is:
    stty 600 ixon ixoff -ixany -parity -tabs onlcr icanon clocal cread -inpck opost 0<&1

    echo "\033.P1:" 2>&1 #set for xon/xoff

    echo "\033.@;0:" 2>&1	#turn off hardware handshake mode
    echo "\033.I250;;17:" 2>&1	# turn on XON handshake
    echo "\033.N;19:" 2>&1	# set the XOFF character

    shift; shift; shift; shift; shift
    files="$*"
	    for file in $files
	    do
		    cat "$file" 2>&1
		    echo "AF;\000\c"
	    done
    exit 0

I should point out that while I've used other plotters somewhat, and have
done lots of work with lpsched, I don't know a whole lot about this plotter
and I didn't write this interface (although I've been tweaking it lately :-)
-- 
Tim J Ihde				INTERNET:   tim@attdso.att.com
(201) 898-6687				UUCP:	    att!attdso!tim
"Blimey - this redistribution of wealth is more complicated than I'd thought!"
		- Dennis Moore and various Presidents