[Gumstix-users] =?us-ascii?Q?AW:_=5BGumstix-users=5D_Proposed_RobostixT_Schematic_and_con?= =?us-ascii?Q?nector_layout?=

[Andreas T. <li...@da...>]

Hi there,

Just my 2 cents... 

> 1) You'll see that we are thinking of using SPI in a way that would
> allow a software download over SPI (NSSP on the gumstix side) if you
> take advantage of the Power-on-reset autodownload over SPI.  On this
> board we have a LDO between the V_BATT (Power Jack) and the supply to
> the ATmega128.  So: dropping L_DD14 will drop the AT power enable, and
> dropping L_DD13 will drop nPROG_EN.  If the programming_enable line is
> low when the chip powers back up it will download boot code 
> over the SPI.
> 

Which LDO are you planning to use? The MIC5255 datasheet i found, didn't
show up a version with 5V output. 150mA output power is also way to small
for hooking up a lot of sensors. 

The ATmega128 don't uses default SPI lines for ISP programming. You have to
connect PE0/PE1 to the gumstix if you want to program the AVR that way.
Otherwise you will need a bootloader. PEN is only needed to enter ISP mode
if you cannot be sure that SCK stays low during power-on reset. Usually only
ISP_MOSI (PE0), ISP_MISO (PE1), ISP_SCK (PB1) and RESET are needed. Have a
look at the chapter about 'Serial Downloading' in the datasheet. 

> 2) Errata pertaining to the schematic passed:  the high-side 
> supply (5V)
> the voltage-transceiver will be pwered directly by V_BATT and not Vcc5
> as noted; ATM_PROGEN will not be tied-high because of an 
> internal tie-high.
> 
> 3) What will be most helpful is commentary on the selection of
> connectors.  All that is shown are the pads and at this point,
> tin-posts are contemplated (e.g. Molex 53047--
> http://dkc3.digikey.com/PDF/EU042/0037.pdf )
> 
> 4) I have transceibvers for 2 more lines to signal from pxa 
> to at128 and
> 1 from at128 to pxa255.  Preferences?
> 
> 5) Sadly-- no stackability on this go-round.  Frankly, I'm 
> interested in
> how the I2C support goes before deciding between the number of choices
> for board-addressing amongst daughtercards.
> 
> 6) Choices made:
>      a) No rs232 level from the atmega to the world, and
>      b) No uart connection between the atmega and pxa255, and

I agree with mgross and think that is not a good choice. 

>      c) The form factor is the same as the Waysmall boards.
> 
I'd suggest to go with a bigger form factor. There Would be more space for
additional connectors. I'd suggest further to expose AVRs ISP and JTAG pins.



Regards,

Andreas