Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!ames!ucbcad!ucbvax!CORY.BERKELEY.EDU!dillon
From: dillon@CORY.BERKELEY.EDU (Matt Dillon)
Newsgroups: comp.sys.amiga
Subject: Re: Nothing to do with Amiga and MIDI
Message-ID: <8712292114.AA22022@cory.Berkeley.EDU>
Date: 29 Dec 87 21:14:56 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Lines: 37

:In article <1325@sugar.UUCP> peter@sugar.UUCP (Peter da Silva) writes:
:>First of all, conventional printers (a slow device) typically come with
:>a very fast interface that they can't even begin to take advantage of, but
:>restrictes them (theoretically) to within 6 feet of the computer.
:
:Which is that?  I've operated Centronics parallel interfaces over 50'
:cables with no problem (although I admit this is stretching it a bit -
:20' should be no problem whatsoever.)

	A couple of things to note here:

	(1) Centronics is syncronous, meaning that every byte is handshaked.
	    At 50' it will go quite a bit slower and much less reliably than
	    at 5'.  However, since printers are notoriously slow anyway one
	    usually doesn't see the difference.  A similar unshielded and
	    undriven serial cable would not be able to go quite as fast.

	(2) Beyond popular belief, serial is NOT slower than parallel!  That's
	    right!  Consider that serial is just two lines (not including 
	    ground)... very easy to make into a twisted pair, shield, connect
	    to power drivers, or place on a carrier.  I've seen serial over
	    a cable TV channel at 56KBaud, and we weren't even trying!  Of
	    late we've had RS422 which utilizes balanced lines and can go even
	    faster than RS232.

	Example: Bryce created a product for the C64 to speed up the
	C64<->1541 interface.  He simply connected an extra serial line on
	an IO chip between the two running at (almost) the crystal frequency.
	Without trying he almost beat out my PET<->2031 interface which was 
	using synced microprocessors over a parallel line (read: no 
	handshaking).

	The moral of the story:  You can make a serial interface sooo fast that
	you don't even have to worry about 'waiting' for the character to be
	sent... the interface is faster than the fastest you could shove it
	out from a lowly 68000.

						-Matt