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About COM Express

mulfycrowh , 08-25-2019, 09:25 AM
Hi everyone,

It is not so easy to understand the differences between Type 2, Type 6 …
As far I understand, new release of COM Express is 3.0 and involves Type 7.

I would like to develop a carrier board allowing external GPU board.
I downloaded the COM Express Carrier Board Design Guide on www.picmg.org. It is bases on release 2.0.
The question is: should I use Type 2 or Type 6?
In the documentation, they speak about a signal on pin D97 (Type 6) named "PEG_ENABLE#".
Why don't we find such signal on Type6?
The Purpose of this signal is to tell that we use internal GPU or not.

Thanks a lot.
robertferanec , 08-26-2019, 09:08 AM
I do not remember exactly, but you may need to choose based on peripherals you need (2 looks like an old one, 6 looks more suitable for today's boards) and on the module you would like to use. This is what I found (simple comparison) - is this what you mean? https://en.wikipedia.org/wiki/COM_Express

mulfycrowh , 08-26-2019, 09:41 AM
That's a good start for an answer. Peripherals are standard. What I do not understand is that signal
on Type 2 that is not present on Type 6.
mulfycrowh , 08-26-2019, 09:45 AM
For MXM board, you'll use PEG Signals (16 lines).
The other PCIE lines will be used for SSD and wireless board.
robertferanec , 08-28-2019, 05:01 AM
When I was not sure how to connect some signals, I always had a look at schematic of the other baseboards which were supported by that specific module.

PS: I do not know why the signal is not on both, probably it was not needed (?) e.g. card can be enabled in BIOS or by some other different ways (just guessing)
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