Theoretically - could this work?

[Sylvain Cote]

Have you tried to use it in manual mode ?

Code:

MANIO     (Manual I/O)
1         (device position in the loop, your RS-232C interface)
SELECT    (select the device)

optional: clear MAN/NORM/TRACE printer flags

Code:

CF 15
CF 16

test GP-GL command

Code:

PINIT     (create Plotter module I/O buffers and should select the first pen)
0
PEN       (plotter select the pen 0 = release pen)
PCLBUF    (clear Plotter module I/O buffers)

edit: test HP-GL command sequence