🚀 go-pugleaf

In article <48@qmsseq.imagen.com> pipkins@qmsseq.UUCP (Jeff Pipkins) writes:
>In article <218@cmic.UUCP> garvey@cmic.UUCP (Joe Garvey) writes:
>>I was told by a vendor that the Centronix interface in a typical (Laserjet II)
>>interface would only transfer data at about 50 Kbaud (yes I know it's byte
>>wide, but it's easier to compare to a serial interface this way).
>
>Using a typical PC (what does this mean anymore?) running DOS, the 
>Centronics interface is software bound.  You can expect to get a maximum
>of about 1K bytes/sec (equivalent to a 9600 baud serial connection).
>A program that drives the port directly (*NOT* reccommended) can reach
>speeds that violate the Centronics timing specs.
[description of DOS driver replacement deleted...]

Seems that I remember that the original Centronics interface spec was
4us/byte (250Kbytes/sec). For 132 characters, then the paper had to
move, and 60lpm was real good. 60x132 characters/min = 132characters/sec.
Not too big a load and not likely software bound :-). Tempting for the
printer manufacturer to use one little Z80 chip instead of a whole big
board full of disrete logic to do the job. And while they're at it, might
as well do graphics and better fonts than the 101A, and wouldn't laser
engines be nice, and how about full page graphics and page description
languages, and the thread runs on like this sentence.

The Z80 became bogged, 2.5Kbytes/second typical rate for accepting data,
but that's fast compared to the printers (up to 300lpm or so) that were
using it. Use more Z80's in one printer, maybe better use one bigger CPU.
The 68000 can get bogged, too. Especially when called upon to manage the
print engine, the font generation, the page description language, the
host interface, the protocol, the coffepot, and whatever else is in printers
these days.  The work expands to bog whatever the CPU is.

For vector graphics, 1000 vectors/second converted to 300x300dpi bitimage
isn't too atypical now. In fact, maybe a bit fast. If a vector takes about
5 bytes to describe (13 for QUIC(tm), less for 4014(tm), less still for others),
then 5000 bytes/second is what the printer will accept when doing vector
graphics. Font management and generation can be a real sponge of CPU power.

The process gets even more complicated when something like POSTSCRIPT(tm)
can take 2MB of data to generate one lousy dot on the page (if you're
clever :-) or a dozen or so lines can take a day or so to produce one
page. I like bytes/hour as a unit of data transfer.
--
Mike Murphy  Sceard Systems, Inc.  544 South Pacific St. San Marcos, CA  92069
mrm@Sceard.COM        {hp-sdd,nosc,ucsd,uunet}!sceard!mrm      +1 619 471 0655