Path: utzoo!utgpu!news-server.csri.toronto.edu!clyde.concordia.ca!uunet!snorkelwacker!mit-eddie!uw-beaver!ubc-cs!alberta!atha!lyndon
From: lyndon@cs.AthabascaU.CA (Lyndon Nerenberg)
Newsgroups: comp.lang.postscript
Subject: Re: 7 vits vs. 8 bits (again)
Message-ID: <1975@aurora.cs.athabascau.ca>
Date: 4 Jul 90 23:57:04 GMT
References: <2414@acorn.co.uk> <1990Jun23.184530.1326@cbnewsl.att.com> <184@heaven.woodside.ca.us> <1363@chinacat.Unicom.COM>
Organization: Athabasca University
Lines: 70

woody@chinacat.Unicom.COM (Woody Baker @ Eagle Signal) writes:

>To answer this, lets first deal with XON/XOFF.  Under DSR/DTR mode (which
>you can set along with 8 bits), you don't need XON/XOFF.  Under DSR/DTR
>mode XON/XOFF should be allowed through.

Woody, you should check out the real world before making assumptions
about peoples communications environments. In our building, we have
about 300 serial lines. They connect printers and terminals to the
computer room. This involves running a LOT of cable. Have you checked
the price of eight conductor cable versus that of three or four conductor
cable? If you had, you would see that the cost of our wiring plant would
have doubled had we run eight wire cable, just to provide hardware
handshaking for 10 or so postscript printers out of 300 devices.

Of course, you could run eight wire cable to the printers only. The trouble
is that printers move, but cabling doesn't. The costs of moving a cable,
or running in a new one are prohibitive. Try keeping your physical plant
documentation up to date when everything is the same, except for this
one over here ...

>The second part of this, such
>as terminating a job, is what the hardware control lines are for.  The
>break key (Not necessarily on a PC) sends a signal (I think it locks
>the line in either space or mark for 500 ms or so) that would serve 
>nicely to stop the printer, or allow you to regain control.

Again, you should investigate the real world. Nearly all our serial
lines pass through a PACX on their travels between the mainframes
and the peripherals. Sending a break through the PACX suspends your
current session and returns you to the PACX command processor. Using
break like this is fairly common in communication switching equipment.
Needless to say, this type of behaviour is going to confuse your spooling
software to no end ...

>What
>I would do, is to make the input routines smartenough to check for
>an ESCAPED sequence to force end of program, and queries.  An example
>might be based on the OCTAL escape sequence hander \ooo, but would
>be \0xHH.

Using '\' as an escape character isn't much different than using ^D.

>The input routine would translate \0xHH into an internal
>byte that would then terminate the job, or return status etc.  the
>\ooo would be translated directly into binary, rather than passed
>thorough as "\ooo".

>I personaly favor
>using hardware control lines to handle handshaking, and break control.

So do I, but only where it's *practical* !

>look at the result for the switch handling procedure.  My point is and
>has been that Adobe should have made the language fully 8 bit transparent,
>or at lease provided an operator to allow this capablilty, and DOCUMENTED
>it.

As Henry Spencer mentioned, the proper way to allow for FULL eight bit
transparency is to implement it inside a documented protocol. The reason
you can ship eight bits inside of Appletalk is that you are using the
facilities of that protocol to get the bytes through. I don't think
Appletalk was the best protocol to use, but that's a whole new barrel
of snakes.

-- 
     Lyndon Nerenberg  VE6BBM / Computing Services / Athabasca University
         {alberta,cbmvax,mips}!atha!lyndon || lyndon@cs.athabascau.ca
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