Xref: utzoo comp.sys.ibm.pc:18996 comp.text:2434
Path: utzoo!attcan!uunet!lll-winken!lll-tis!helios.ee.lbl.gov!pasteur!ucbvax!decwrl!labrea!glacier!jbn
From: jbn@glacier.STANFORD.EDU (John B. Nagle)
Newsgroups: comp.sys.ibm.pc,comp.text
Subject: Flow control between IBM PC and printer
Keywords: DTR DSR XON XOFF Postscript Laserwriter
Message-ID: <17697@glacier.STANFORD.EDU>
Date: 11 Sep 88 16:27:00 GMT
Organization: Stanford University
Lines: 29


     I'm losing characters between my PC and Laserwriter.  I assume that
I have flow control problems.  The present setup is:

	PC is running the standard DOS 3.1 PRINT program and driver.
	The cable connection between the PC and the Laserwriter
	has a null modem box from 3M, with

		TX1  -> RX2
		DTR1 -> DSR2
		CTS1 -> RTS1, DCD2

		TX2  -> RX1
		DTR2 -> DSR1
		CTS2 -> RTS2, DCD1
		
	3M calls this a "standard null modem".  It seems strange, in that
	flow control is normally provided via RTS/CTS.  Yet the Laserwriter
	documentation indicates that the Laserwriter tries to do flow
	control on DSR/DTR, which is nonstandard.

	The Laserwriter (a IINT) is in DSR/DTR mode, 9600 baud.
	Postscript files (which are not missing characters) sent to the
	printer lose 1 to 10 characters on rare occasions, perhaps once
	every few pages.

	What are the PC printer conventions on flow control, anyway?
	Where is this documented?

						John Nagle