Thursday, 13 March 2008

Part 1 update gets sensible

One of the issues that I have been on about is that Equipment Phases are only phases if they directly relate to the Recipe Phases. I always believed that the original Part 1 says as much, and more than that that the people who wrote it meant it that way.

Somehow over the years some people seem to have not understood that, but I am very pleased to hear that the update commitee has re-affirmed it. Here it is:

General Discussion – What makes an EM different than a CM?

The entire call was spent discussing the equipment module / control module clarification. Key agreement was that an equipment module could have two forms of procedural control logic. First, it is clearly stated in the standard that EMs are the lowest part of the physical hierarchy that can perform procedural control and thus have an equipment phase. By definition, this type of procedural control logic is intended to be directed by a recipe phase and that association should exist. It was also agreed that there may be another type of procedural logic which may be performed by an EM which is not directed by a recipe phase. In this case, such logic should not be called an equipment phase, but some other name (possibly “equipment task”). This non-phase related procedural logic may be commanded by operator interface or by another (possibly superior) EM. The key difference then from a control module to an equipment module is this capability and existence of procedural control logic. Control modules do not perform procedural control. An equipment module is used to support the lowest level execution of procedural control, either as directed by a recipe phase (causing an equipment phase to process), or as directed by a non-phase entity (causing some currently un-named procedural logic to process).

Personally I would have gone further and reserved the word procedural as belonging to the recipe as well, and found another name (perhaps sequential) for the second type of equipment control. But it is better than it was looking a few weeks ago.

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