<As an aside, there have been laser printer interfaces where the host
<computer gets to control the laser engine control signals directly,
<rather than talking to a 'formatter board' that turns
<text/graphics/postscript/whatever into a suitable bitmap for printing.
DEC LN03P (~1988), a video print engine. Used a bit map in the host
computer wuth serializer, there is still a small embedded micro to cotrol
the basinc mechanics. FYI: due to construction and process laser printers
have to keep the paper moving or the image will be a mess.
The most extreme was the LPS40 (DEC, 12/27/1997) that literally had a
BA23 microvax in the base to do, networking, distributed queue management,
Postscript to raster engine interpretation. It was then handed to a 4board
set (bimaps and display list to raster bitmap engine) and set serially to
the printengine. The printengine had 1 8085 to manage the system, 3 8749s
to manage the mechanics and a 78pg11 to handle the large capacity paper
input. All that was to print complex postscript pages at 40ppm. That
seems obscene but starting one piece of A4 paper every 1.5 second plus
between three and four peices in transit is not a trivial task. Then there
was the Xerox 9700 (120ppm) monster (10+running feet of laser printer.).
<Of course this is a slightly higher level than talking to the mechanics
<directly, since you have a signal to tell the printer to start a page
<rather than having to control the motor and clutches directly. But still,
<the host computer has to monitor the Beam Detect signal and send suitably
<timed pixels to the laser control input.
Beam detect is a sync signal and it's all done in hardware. You get a sync
and start DMAing data to a serializer at a preset clock rate. Not much
different than driving a tube.
<I've seen (and probably still have somewhere) plastic daisywheels with a
<metal pin for the '.' , just to make the last a little longer when used
<like this.
My first plotter was a modified daisy mech, no daisy and a pin brazed to the
solinoid. Good to 200 dpi or so.
Allison
Received on Sat May 29 1999 - 11:07:59 BST