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From: "Pat Ford"
Subject: Re: Avoiding PLCs
Date: Thu, 17 Oct 2002 16:02:33 -0400
Organization: National Research Council of Canada
References: <firstname.lastname@example.org> <email@example.com>
NNTP-Posting-Date: 17 Oct 2002 20:02:29 GMT
X-Newsreader: Microsoft Outlook Express 5.50.4807.1700
"Bill Shymanski" wrote in message
> Backward compatiblity? Oh really ? Where can I buy:
> - 5 1/4 inch disk drives
do you have software that requires a 5.25 drive? I have 2 8" drives at home
(working too)dos6.22 recognized them, I cant remember if I tested Dos 7
> - MFM hard drives
do you have software that requires a MFM drive?
> - 5 1/4 inch floppy disks!
do you have software that requires a 5.25 disk?
> - XT-compatible keyboards
Yes I can.
> - Anything that can plug into an AT backplane
this one is even sillier then the 5.25 drive, Yes I can.
> - An EGA monitor
do you have software that requires an EGA? Some poorly behaved s/w writes
directly to EGA ports, but thats a programmer that did it not an overall
> etc. etc. The PC is a moving target and can't be maintained for more than
> a couple of years. New laptops don't even come with RS 232 ports!
laptops aren't really designed for industrial use but you knew that.
> One of the reasons a PLC is a Z80 in a $5000 box is that you'll be able to
> buy replacement parts for it for
> 20 years. Most control applications are not processor-limited. ( Yes, I'm
> aware that more powerful processors are available in PLCs but there's
> still thousands of Z80s out there doing the world's work.)
> A cheap desktop machine isn't even fit to be used on a desktop. By the
> time you "harden up" a PC to be useful for control applications, the darn
> thing costs as much as a
> real PLC and crashes roughly 3 orders of magnitude more often.
??? I know many people who well be dismayed to hear this ( some with systems
that have been running for 15 years). Don't confuse OS induced problems with
> The only time I crashed an Allen-Bradley PLC 2 processor was when I
> delibrately did something that a recall notice told me would stall the
> processor. Desktop PCs stall...a lot more frequently.
goes to O/S problems, not using the protected memory that every PC from 386
up has. If I run a solid RTOS ( I worked at QNX, but most other PC RTOS's
are just as good) I cant crash the system without deliberate attempts
> Now, a PC, doing all the data logging and sending data to your networked
> office automation system, standing between the "office" world and the PLC
> world, is a really good thing - and you don't mind replacing it every
> couple of years.
Why would you? Gamers and the like need the fastest crap, real work systems,
once working don't need upgrades. I have machines at home running win3.XX
why, they don't need more.
> Of course, if they stop selling PCs with serial ports,
> it's going to be really hard getting it to talk to that 1770-KF2
> "Pat Ford" wrote in message
> > One reason is that PC's will be available for a long time, and
> > have amazing backwards compatibility. I can still run some programs from
> > at on my 2GHz machine. Another reason is that they are available no 30
> > delivery. The processing power in a modern PC combined with the low
> price is
> > also a good reason.
> > As far as a 3 month PC being obsolete may be true but the software
> tends to
> > still work and why upgrade if it works.
> > Pat
> > "Kevin Carney" wrote in message
> > news:firstname.lastname@example.org...
> > > I am just lurking but here is my $ 2 (adjusted for inflation) . With
> > > the rapid changes in the P.C. market (operating systems, hardware
> > > etc.), Why would a company want to put a PC as the controller for a
> > machine
> > > they may use for 15 years ? What if the PC poops after 3 years, you
> > be
> > > able to get the same interface cards to work with a new operating
> system ?
> > > My thoughts are that the latest and greatest every 6 months,
> obsoleting a
> > 3
> > > year old PC has killed the PC market. People aren't going to spend $
> > > every 2-3 years for the latest & greatest.
> > >
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