Just thought you might like a look at a real PLCgreenspun.com : LUSENET : TimeBomb 2000 (Y2000) : One Thread
This link goes to an information site maintained by Radio Shack. This is about a product they have added to the hobby line of electronics - a small PLC that can be programmed in BASIC. Nice little gadget - thought you might like a look at what all the fuss has been about.
-- Paul Davis (firstname.lastname@example.org), December 03, 1998
I couln't read everything in this site, but a search for "dates", "2000", "real time clocks" and a few other key words yielded nothing about year 2000 compliance - other than the PLC's reliance and use to the external RTC and BIOS.
And this is for a company that still makes the thing, is trying to sell it, and has up-to-date info. Imagine trying to get info about a controller from a company gone out of business, or overseas, or overseas and out of business after Jan 2000......
For another example of remote sensors and controllers, see Rosemount's catalog and web page. These are very typical of what are used in power plants, refineries, and chemical plants.
Rosemount is year 2000 compliant (now) but just recently upgaded its control programs and functions. Nothing sold earlier (before Dec 1998) was compliant. Actual dates in the older instruments will okay., once they are "reloaded" from the outside program for repair dates or whatever.
The "sensed" information goes to the central cmputer as a signal - and any control function that would be needed (that could be date sensitive) is strictly controlled by the central (non-instrument) program.
Whether or not each customer has changed, or needs to change, his program is beyond Rosemount's control.
-- Robert A. Cook, P.E. (Kennesaw, GA) (email@example.com), December 04, 1998.
Actually the stamp is Y2K compliant, you just missed that section. It has no timing function beyond the internal tick function for synchronizing the various parts of the PLC - no timing at all otherwise and you can't get to that timing function except as a countdown/up. If you need other timing functions you must add other chips to provide them. All of Intel's CPU chips are Y2K compliant for exactly the same reason - they have no built-in timing functions at all. The problem lies with the BIOS and other chips external to the CPU chip i.e. a motherboard based on an Intel CPU may not be Y2K compliant - but the CPU will always be Y2K compliant.
-- Paul Davis (firstname.lastname@example.org), December 05, 1998.