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Date: Wed, 9 Oct 2024 21:29:09 -0400
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Subject: Re: EMC compliance question
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 <ko3egjh48259s212n8i8dc6jql0vlc9vb8@4ax.com>
From: bitrex <user@example.net>
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On 10/9/2024 7:18 PM, john larkin wrote:
> On Wed, 9 Oct 2024 19:03:28 -0400, bitrex <user@example.net> wrote:
> 
>> What's the deal with the "CPU board" exemption?
> 
> Where is there such an exemption?

It's under the section on sub-assemblies:

<https://www.ecfr.gov/current/title-47/part-15/subpart-B#p-15.101(e)>

A "CPU board" as defined previously is considered a type of sub-assembly.

As a hypothetical say someone sells a product that's a PCB with a PIC on 
it and some relays that has e.g. RS-232 port and terminal blocks to 
connect to other stuff. It's in some sense a functional product, but the 
user must at least connect it to some load of their choosing for it to 
actually do anything. And they can put it in a housing if they wish, or 
not, whatever.

Is this still a "sub-assembly"?


>> "CPU board. A circuit board that contains a microprocessor, or frequency
>> determining circuitry for the microprocessor, the primary function of
>> which is to execute user-provided programming, but not including:
>> A circuit board that contains only a microprocessor intended to operate
>> under the primary control or instruction of a microprocessor external to
>> such a circuit board; or
>> A circuit board that is a dedicated controller for a storage or
>> input/output device."
>>
>> So if one sells a board that has say a PIC on it and some support logic,
>> and the 9kHz+ signals are all internal to the uP (self-clock), but it's
>> otherwise a functionally complete design other than it's not in a
>> housing, is that an exempt product?