Serial port config'n

[Gary Horton]

I'm on a Sparc 1+, running SunOS 4.1, and am attempting to
send bytes via a serial port to an HP PaintJet to 
accomplish raster graphics. I have determined that zero-filled
bytes cause confusion.  Baud and parity are fine (9600, none)
and I've used library routine ioctl() to configure the port
for 'no post-processing'.  All other values produce the
expected raster image; does anyone know what to do to 
render zeroes usefully?  Somewhere I've heard that serial
ports discard null characters unless instructed otherwise.
Oddly, with same serial port configuration, I do NOT have
this problem on an HP9876A Thermal Printer (the only diff. 
being baud here is 19200); ergo, I did not initially suspect
the port config'n.  Could it be on the printer side?

Please send replies directly to me; thanks very much for any
help!!!