Proposed Expansion Module Standard

mctrivia · 2009-10-16 13:52

I propose that the PCI Express Connector be used as a standard method of adding expansion modules with the pinout attached.

Reasons:
1) available in both through hole and surface mount:
Surface Mount: 10061913-102CLF
Through Hole: 10018783-10202TLF
Board Edge: NWE49DHRN-T941

2) Connectors are fairly cheap and no headers are needed on expansion module

3) Lots of pins: 98

4) If Expansion and in system programing is not needed the connector can be cut off to reduce board foot print

5) I will be releasing a module using this pinout soon that has:
*512Mbit RAM
*IDE Interface
*HDMI Output
*IO Expander

Of course 5 is a personal reason but the first 4 are good reasons and a standard method makes modules more usable.

Notes on Pinout:
P0..P15,BOE,RES are prop pins. arrangement is to allow easy trace running with connector to the left of the chip.
There are 2 power rails. Top right is 3.3V. Bottom left is optional 5V/12V rail. I have labeled as 5V because I am using it as such but in my test rig I have set this as 5V or unregulated 12V with a jumper select. In my module only the HDMI output requires the 3.3V rail.

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Mike Green · 2009-10-16 14:30

IMHO, the "market" will determine what kinds of "standards" are appropriate. This (PCI) suggestion is a good suggestion to try for some applications and some possible expansion boards, but it's not a good idea for most uses of the Prop I. The Prop II with its additional I/O pins may be a different story.

Part of my objection to this for most applications is that a lot of the Prop I/O pins are usually used for specific fixed purposes like VGA output or PS/2 inputs. That can cut down the 32 I/O pins quickly to 16 or less where a smaller connector, possibly just a 10 x 2 or 16 x 2 0.1" header will do and is cheaper and smaller.

Rayman · 2009-10-16 14:38

I was looking at the ISA bus standard for some ideas... I think an 8-bit bus is more up the Prop's alley...

BTW: I think it' be neat to have a Prop on a real PCI card...

BTWA:· I'm looking forward to seeing if you can get HDMI out...· I have a design for DVI output, but haven't found the time to get a board for it yet...

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mctrivia · 2009-10-16 14:45

yes the smaller headers are cheaper for through hole. in surface mount they can get pretty expensive and this way only 1 header is needed not 2.

You are right abour pin count being limited. How about we say that the prop pins don't all need to be used.
P0-P3 is called 4x
P0-P7 is called 8x
and P0-P15 is called 16x

Just like PCI Express in the computer which can come in 1 to 16x Board designers can design for 1 of these setups and any module below or equal to the board limit will work. Designs like mine that use a CPLD as there core can be reprogrammed to offer all options.

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mctrivia · 2009-10-16 14:47

Ya I am placing the pads for the HDMI parts and carefully running the traces but in the end that option may just be unpopulated pads. I was originally going for VGA but the head is to big and I want true digital. I settled on HDMI because both HDMI to DVI and HDMI to VGA cables are readily available.

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waltc · 2009-10-16 16:10

I have to agree with Mike Green on this. PCI bus is good for certain kinds of apps but not all of them and the "market" will be the final decider on whether its good or not.

mctrivia · 2009-10-16 16:19

just to make it clear i am not proposing using a pci bus format but using the pci express connector as the standard for expansion modules. i am not using the connector correctly.

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Phil Pilgrim (PhiPi) · 2009-10-16 16:42

Standards always follow the market; they never lead it. If you want to set a standard, create a bunch of boards that use it. If people like it, then others will design more boards to the same specs. Then someone else will come along and give it a name, like "PropCI", or somesuch. Before you know it, all the industry pundits will be chattering about PropCI. That's how standards come about. But just saying "let's create a standard" before any products are put on the market is not going to get anywhere.

-Phil

SRLM · 2009-10-16 16:47

Perhaps a better way to look at it is to say: "Would this design meet all the criteria for a standard?"

mctrivia · 2009-10-16 16:54

Phil Pilgrim: well my modules are going to the fab shop tomorrow so there will be boards using this layout soon. I thought I would give my reasoning and make it publicaly known so anyone that wishes to make a prop board with expansion capability could consider it before they get pcbs made.

By doing so Mike has already made a good point that in my design consideration i should make sure that people can use with smaller buses also.

SRLM: good point. Is there anything I am missing?

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Rayman · 2009-10-16 17:49

mctrivia said...
both HDMI to DVI and HDMI to VGA cables are readily available.

HDMI to DVI and back is just connectors and wire.

But HDMI to VGA would need need special some chips...
I'm not sure I've seen an HDMI to VGA adapter...

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jazzed · 2009-10-16 17:49

Among the current alternatives:

- The spin studio "bus" idea is cute (however restricted) and meets most of the market amateurs' needs.
- "Morphebus" seems closer to a truly useful standard than anything else I've seen for Propeller.

I agree with SRLM
As one example: The PC "pick a part" architecture "standard" is useful because many vendors parts work in the functional elements and expansion options are essentially limitless. You should study that successful model.

>> Is there anything I am missing?

Market/pundit driven arguments aside

... I'm baffled that you have put all your pins on the small connector. That's fine if you only have a small connector. How would the rest of the connector be used? At minimum it seems that all Propeller pins except crystal would be on such a connector. Whether they are used or not is up to the "user" [noparse]:)[/noparse] Since you have chosen a "bus" connector, it seems appropriate that a real bus should at least be defined. I suppose that could evolve though.

The Basic Stamp board APPMOD connector enabled many people to sell many boards. Of course it was defined by Parallax, so the pundit arguments were null. The problem with trying to define a standard up front rather than being dragged into one by the market is in avoiding making camels (horses designed by committee).

All of that being said, however, it's probably best to just do what you think is right for your product and forget everyone else's opinion

mctrivia · 2009-10-16 18:25

jazzed if you look at the bottom of the diagram you will see that i have defined all the other pins to io expansion though for this particular product the last 10 on each side will not be doable.

For my particular product the actual use of any 1 pin does not mater. My test rig is wired up as shown in the picture but since all pins go to a cpld all but the jtag and reset pins can be reprogrammed on the module.

I suggest it as a standard so products like Rayman PSB could place the connector on now. I will be designing an adapter for Morpheus so it can be used with that.

As for why I put all the major pins to the small part is so that for products that do not need in system reprogramming or io expansion they cut that part of the connector off(I know 22 pin pci express connectors exist but i can't find them) and use that space for running of traces or placement of low clearance parts(tall parts would interfere with the rest of the module)

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Phil Pilgrim (PhiPi) · 2009-10-16 18:34

mctrivia said...
I thought I would give my reasoning and make it publicaly known so anyone that wishes to make a prop board with expansion capability could consider it before they get pcbs made.

If you wanted to foster this process, you could create a proto expansion board for your bus with the connector pinned out, along with some power and ground traces. That way people can try their circuits before committing them to PCBs.

-Phil

jazzed · 2009-10-16 18:36

If you're talking about the conector.png from your first post, I see an overwhelming number of empty pins.

Are you suggesting people buy connectors and hack them up? That would render them mechanically unsound.

It is nice that Rayman has created a market for LCD breakouts. It seems your best immediate opportunity is selling those especially when everyone realizes how difficult it will be to solder that flex cable [noparse]:)[/noparse].

mctrivia · 2009-10-16 18:40

yes in conector.png in the bottom right there is a note saying all unassigned pins are io expansion.

you both have very good points.

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Nick McClick · 2009-10-16 19:07

Few thoughts;

A lot of people use microcontroller projects in rough environments. Does the pci-e connect provide a firm physical connection (will it survive strapped on to my bike for a few weeks?)

How much current can go thru the 5V and 3.3V connectors? What if the motherboard is supplying current to a daughterboard that's running servos?

If you're doing a board with a small footprint but still want 5V, are you stuck with the full connector?

I like doing board edge connectors - pin headers / sockets are pretty expensive

Does the standard include how you stack modules (and where the connectors should go) or just the connector?

I'm 100% pro-standard, and there are already a few 'standards' out there. Of course, the market can support multiple standards and it gives the designer flexibility to use the right tool for the application.

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mctrivia · 2009-10-16 19:24

the entire connector is only 2" long which is another reason i chose it. If you want 5V you can either use a boost converter or use the full 2" connector. I could define pin1(currently unasigned) as 5v also but it would not properly hotswap. I would think a chip select would be more useful use to allow a bus configuration.

if memory serves me correctly 1.1A but i can't remember where i saw that.

if the daughter board is running servos i would recommend using an auxiliary power connection

there are locking connectors available but the module needs to be designed in a special way to use them. the full 96pin connector is fairly mechanically strong and will not easily vibrate out.

My thinking is each board would have only 1 connector. I was not intending it to be used as a bus though it would work if pin 1 was defined as a chip select.

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ziplock · 2009-10-16 20:12

I've been working on my own Prop board, and was thinking about expansion. I decided that PCI wasn't a good choice, because things like SpinStudio's connector and Morphbus already exsist. It's wiser to use something that's already around than to create your own. For example, what if someone thought your board was cool, but a key deciding factor was backwards compatibility? It'd be wise to either use something that's tried an tested, or include something that already exists AND use your own connector.

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mctrivia · 2009-10-16 20:18

This allows me to make 1 board that surface and through hole both work well and gives me lots of io pins.

If you use spin studio or morphbus I will make an adapter so you can still use my module.

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Proposed Expansion Module Standard

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