Path: utzoo!mnetor!uunet!husc6!mailrus!ames!killer!elg
From: elg@killer.UUCP (Eric Green)
Newsgroups: comp.sys.amiga
Subject: Re: Amiga as workstation (serial ports, really)
Message-ID: <4031@killer.UUCP>
Date: 9 May 88 05:26:23 GMT
References: <8805051951.AA26195@cory.Berkeley.EDU>
Organization: The Unix(R) Connection, Dallas, Texas
Lines: 45

in article <8805051951.AA26195@cory.Berkeley.EDU>, dillon@CORY.BERKELEY.EDU (Matt Dillon) says:
> :What, huh??  I've never seen anything shove bits as fast over a serial line
> :as you can over a parallel line.  Try comparing the time to download fonts
> :to LaserJet II on parallel vs. serial (even at 19.2Kbaud) sometime, and see
> :if you don't want to keep your parallel port around when you get a laser 
> :printer.
> 	Ahh hah haa ha.... Man, you haven't seen serial lines.  There are
> 	a couple reasons people use serial rather than parallel.  When I
> 	design *any* custom communications hardware, I always use serial.
> 
> 	(1) You can do it with a twisted pair, and only two drivers on either
> 	    end.  Or at worst three wires (full duplex operation).  With 
> 	    full duplex I usually run data communication synchronously.
> 	(2) You can run the things *fast* ... So fast, in fact, that in
> 	    many cases one doesn't even need to check the TxRegister Empty
> 	    bit... the bits gets shifted out faster than you can write the
> 	    port.
> 
> 	It isn't my fault idiot manufacturers are still running their
> 	serial ports at 19.2KB.

As an aside, I've seen an Amiga shift data out its serial port at
320Kbaud. Wasn't much machine left over for users, though :-). 

I suspect that the main reason that "idiot manufacturers" still run their
serial ports at 19.2Kbaud is because most commercially available (= CHEAP)
UARTs are only capable of 19.2Kbaud. For example, the 6551, which is cheap,
has low chip count (add a crystal, bus buffers, and ready to go), and is
easily interfaced with 68xx/65xx/68K-based machines. I suspect there's an
aweful lot of 6502's out there (e.g. I recently discovered that the TVI 910
was 6502-based, when I patched a bug in their firmware for a local
university). 

Higher bitrates seem to require either more expensive chips, or custom chips
like in the Amiga.... and, of course, there's always the ULTIMATE in bitrates,
fiber-optic Ethernets at 5 megabaud and up.

But for a low-cost interface for modems and printers, I suspect that 19.2kbaud
is going to hang on for quite a while (at least until 38kbaud equipment
becomes more common).

--
    Eric Lee Green                     {cuae2,ihnp4}!killer!elg
         Snail Mail P.O. Box 92191 Lafayette, LA 70509              
"Is a dream a lie that don't come true, or is it something worse?"