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PLC PAC operating system

I realize this is an ancient thread, but I'm also trying to figure out whic h OS Siemens is using in the S7 line. I know Rockwell's ControlLogix and Mi croLogix are both VxWorks, and their older PLCs are Microware. B&R is all V xWorks. Beckhoff uses Windows CE or Windows Embedded with RT. VxWorks is th e clear leader since mid 2000's to now and there is a fairly good chance th e S7s are running it, but Siemens has used RTX on some other products, so t hat might be it as well. There are a lot of people saying S7 is a home grow n kernel, but I can't imagine that is true. More likely such assertions are ignorance (similar to the asinine first several responses to the original question).

The idea that a PLC somehow does not need an OS just shows a fundamental mi sunderstanding of what a PLC is an OS is or both. Take a look at the wikipe dia page

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I guarantee more than 99% of PLCs in production use one of the packages in that list.

Reply to
isaac.a.brown
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As it turns out, Siemens did make their own in-house RTOS for the S7 platfo rm and there are rumblings that they put in the Basisk backdoor admin passw ord to facilitate the creation of Stuxnet. Anyway:

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Reply to
isaac.a.brown

Why would a single loop PLC need a real time kernel ?

After executing the program, it either restarts immediately or after the next clock interrupt ?

After all, the PLC is quite similar to a DSP application. The PLC application executes the same applications a few tens or few hundred times a second, an audio DSP executes the program perhaps 48000 times a second.

Reply to
upsidedown

The referenced presentation (quite interesting, by the way) explains that a high-end/high-speed PLC performs control of several kinds: Current Control, Speed Control, Position Control, Kinematics Control, and that these controls are executed at different frequencies, with Current Control highest frequency, Kinematics control lowest.

A pre-emptive RTOS may thus be useful.

--
Niklas Holsti 
Tidorum Ltd 
niklas holsti tidorum fi 
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Reply to
Niklas Holsti

Even the low-end PLCs these days usually support one or more Ethernet interfaces and a half-dozen protocols (they often include a web server). Even before Ethernet was widespread, there was usually a high-speed serial port or two with various protocols to support connection to engineering tools and SCADA systems.

--
Grant Edwards               grant.b.edwards        Yow! In 1962, you could buy 
                                  at               a pair of SHARKSKIN SLACKS, 
                              gmail.com            with a "Continental Belt," 
                                                   for $10.99!!
Reply to
Grant Edwards

A single loop PLC does not need any RTOS.

Any multi loop PLC would definitively benefit from a good pre-emptive RTOS kernel.

Reply to
upsidedown

Ethernet or fast RS-232/422/485 can be easily handled in ISRs and the applications can be executed in a single non-RTOS systems.

When you have a dozen or two serial or ethernet interfaces,and multiple loops, any RTOS kernel will help a lot :-)

Reply to
upsidedown

Real-time does not mean real fast. Rather, it means the kernel

*makes* timeliness guarantees to the tasks running on it. Even if it is a single thread of execution. The same is not true of an MTOS or even "a big while(1) loop".

Additionally, there may be a single "user loop" but that doesn't mean there aren't other concurrent activities happening "behind the scenes". E.g., communication drivers, "canned" PID loops, "programmer" interfaces, etc. Inputs could potentially be sampled synchronously ("real time guarantees") by the "system" and presented to the user's control loop. Similarly, outputs could be "accumulated" (from that control loop) and presented to the field also synchronously. Hiding all of this from the user/programmer makes his job easier (and less troubled by things like races, etc.)

Reply to
Don Y

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