How do I send a binary file across a serial port?

[Tim Fredrick]

(The following is for an IBM Risc-System 6000 running AIX 3.1.3002)

I want to send an IMPRESS (binary) file to an Imagen printer connected on
a serial port without translating characters, appending headers, or otherwise
formatting the data stream.  I've hacked at the problem for over a month
now trying but failing to understand what data streams go through what
stages if you enter "lpr filename".  Has anyone tackled and solved a similar
problem, or preferably set up an Imagen printer?  If so can you post or
let me know how you accomplished the task.  Thanks in advance.   --Tim