Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cornell!rochester!pt.cs.cmu.edu!sei!gjp
From: gjp@sei.cmu.edu (George Pandelios)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Interfacing serial printers to PCs
Summary: RE:  Re: Interfacing serial printers to PCs
Message-ID: <3504@i.sei.cmu.edu>
Date: 15 Jun 89 03:44:56 GMT
References: <3484@i.sei.cmu.edu> <626@acheron.UUCP>
Organization: Carnegie-Mellon University (Software Engineering Institute), Pgh, PA
Lines: 61

Ed Clarke writes:

>From article <3484@i.sei.cmu.edu>, by gjp@sei.cmu.edu (George Pandelios):
>-    My AT-class computer is unable to print a file at data rates greater
>-    than 150 baud without overflowing the printer's buffer.  This is be-
>-    cause the LQP03 uses an XON/XOFF protocol, whereas DOS implements a 
>-
>-            SUPERSPL  which I believe to be a commercial product.  I
>- 		     was unable to discover who makes it, though.
>
>Hmmm - I've been using the following to drive my LaserJet at 9600 baud.
>The LaserJet uses XON/XOFF protocol:
>
>MODE COM1:9600,N,8,1,P
>MODE LPT1:=COM1

Hmmm, indeed!  That's an interesting twist to the issue.  However, there 
are some other aspects of the two printers that should be considered:

    1.	True printing speed:  My LQP03 is only rated at 25 CPS.
	The LaserJet is substantially faster than that.

    2.	Buffer size (internal to printer):  Again, the LQP03 only has
	a 256 character buffer.  That's SMALL!!!!  I don't know the
	actual size of the LaserJet's buffer, but it's GOT to be bigger.
	I believe LaserJets have a minimum of 512K and can be expanded.
	Is that correct?  Can that memory be used for buffering?

With those two factors in mind, remember that I was able to get the
printer to work without a protocol in place (at 150 baud).  But you
can see why higher speeds are impossible without some sort of handshaking.
I think that explains why Ed's LaserJet is having no problem with 9600
baud.  It simply has the ability to move (print) greater amounts of data
at greater rates.

One other question:  Does the LaserJet possibly implement the hardware
flow control protocol under the covers?  Isn't that how other serial
printers work with IBM PC/XT/AT/Compatibles?  Let's hear from some 
more owners of serial printers.

Thanks for the response, Ed!

George

PS.  Keep those cards & letters coming.  I'm more than willing to send
     copies of XONXOFF.ASM and FLOW.ASM to anyone who wants them.  If
     the volume becomes intolerable, I'll post the sources to all my
     original news groups.

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