Small-footprint Due

If you can include the neglected slave select pin NPCS3 (LFBGA pin A2) for SPI, then it would be possible to use the external decoder support to allow up to 15 peripherals. That one wire could expand SPI peripherals to 4 (or 15 with decoder). It looks like the Arduino software already supports this pin, but its left unconnected on the Due board.

Nice mini-board - I was (am) considering something similar - a mini core board with LFBGA that breaks out all pins.

Thanks guys. Will post schematics shortly.

This IS based on 144 lqfp. Very hard to deal with bga without using very expensive pcb process.

5v is there to allow plug into boards with 5v supply.

Good idea on adding usb pins. Would you want the associated circuitry on this board or leave out for the shield?

Same on the 4th spi Cs pin.

Cost wise I expect $13 all in. Assuming good volume of course

Good idea on adding usb pins. Would you want the associated circuitry on this board or leave out for the shield?

Depending on space. The most important point would be, to have the pins available. If there is space left on the board for the circuitry, the shield would be very easy. Without pins however, the functions are not accessible.
Better leave the circuitry off, if that gives you space for other pins.

Cost wise I expect $13 all in. Assuming good volume of course

I assume, that this should be no problem with a good crowdfunding campaign.

thx. added a row of pins to break this out. circuitry on board so you just need to connect the pins to VUSB, D+, D-, ID, UGND. I wonder if there are some creative ways to simplify addition of the connector to these...

Used some extra space to add 4 additional digital pins and better layout for AREF reference.

gogol:

  • make VDBU available

what is VDBU pin? It's not in SAM's datasheet...

Sorry, I missed a "D": VDDBU ...

gogol:
Sorry, I missed a "D": VDDBU ...

got it. but why would this need to be broken out? why not leave it permanently tied to +3.3V supply?

What might need to be broken out is RTC crystal pads, right? I mean, if we go to the trouble of breaking out NRST, we should make RTC fully functional, right?

valerun:
got it. but why would this need to be broken out? why not leave it permanently tied to +3.3V supply?

Figure 5-3 in the Atmel-Dokumentation shows the purpose, when you wish to connect the backup-batterie like a small coin package. That may need some kind of solder-pad, where the connection to +3.3V can be cutted/solder-closed as needed.

valerun:
What might need to be broken out is RTC crystal pads, right? I mean, if we go to the trouble of breaking out NRST, we should make RTC fully functional, right?

Right with that, but the second advantage is, that the NRST is bidirectional, so that external components can be reset through it.
If you connect the external components to NRST they are reset, whenever the reset-controller resets the chip, even when caused by software! That means, that you need no code, which uses GPIO-pins to reset your peripherals.

gogol:

valerun:
got it. but why would this need to be broken out? why not leave it permanently tied to +3.3V supply?

Figure 5-3 in the Atmel-Dokumentation shows the purpose, when you wish to connect the backup-batterie like a small coin package. That may need some kind of solder-pad, where the connection to +3.3V can be cutted/solder-closed as needed.

Thanks. I read through that section but can't understand if there is going to be any residual consumption on rest of VDD pins if the chip is put into a backup mode... If the consumption is zero on all other pins (chip is down, after all), then one could just keep the battery connected to all supply pins at all times. This does assume that the user would move the chip to backup mode once loss of 3.3v external power is detected (perhaps using one of the digital pins to sense that). But this does sound like a kludge. Will try to break this one out, as well. Running out of space, though :wink:

The SAM has a SHDN pin that is supposed to be used to shut down external regulators, that may imply that this should be done to get the best low power operation, but I think it's just to kill external circuitry, the CPU itself has this well handled.

One would assume as you say that the current used on the VDD pins is next to nothing, in fact if you look at Fig 46-4 they have all the VDD pins shorted to GND for testing the VDDBU current, so it's fair to say there is nothing but some leakage current on those pins under a normal shutdown situation.


Rob

ok got the USB pins out (R5, R6 39R resistors fitted on board but varistors don't fit so a shield would have to implement those).

Also got the VDDBU out (bridged to +3.3v - would need to be cut if this feature is used).

Finally, was able to fit in 32khz crystal and caps - at the expense of one digital pin breakout :wink: I just would hate to have sensitive crystal circuitry broken out via huge 0.1" pins...

All this cost ~8% increase in board size. On the plus side, that allowed adding one more analog and a few digital pins

Will post new board and schematics shortly

...got to stop adding pins...

added one more row on the 109-144 side of the chip which allowed a few additional digital pins but more importantly placing a 3.3v CAN tranceiver to be able to use an excellent CAN-DUE library by collins80 and a few others. These tranceivers run in our EV chargers and work like a charm. So now we have a fully plug-and-play CAN channel on board.

1.4"x1.4" board with 91 pins in 2 rows along the perimeter. The original idea was to have ~40 pins... lol

Sample chips arrived from ATMEL today.

Any other suggestions before we order the first ~10 boards for testing?

V

That really sounds like a boost-board for the DUE-family. A fraction of the size of the original, with an estimated price, where you have not to think about letting the board in a project.

yes, that's the idea.

someone mentioned something about breaking out EBI data bus... What do you guys think about that? Better be very critical as I REALLY don't want to add a third row of pins

just checked - full EBI bus is ~50 pins. so perhaps sometime in the future...

Will you consider breaking out the Ethernet?

would RMII be sufficient? 8 pins way better than 16...

You want to be careful about feature creep, I've done two Due-compatible designs now and in both cases they got too big and complicated so I ditched them.

OTOH it's a shame not to have all the SAM features :slight_smile:


Rob

Graynomad:
You want to be careful about feature creep, I've done two Due-compatible designs now and in both cases they got too big and complicated so I ditched them.

OTOH it's a shame not to have all the SAM features :slight_smile:


Rob

so true...

ok RMII is in. Same board size (just reduced number of ground pins in the corners. Sending to PCB house today