I think what you are saying is the chip you are using uses the Chip Select to
indicate each frame for the SPI transfer. So for every byte you send to your
device you need to toggle the Chip Select. Since the EP9302 does this for you
automatically as you place bytes on in the SSP fifo its not usefull to use a
GPIO for this chip select.
I believe the solution is to use external logic to only operate the chip
select if a designated GPIO is set.
|
> 7400 Ohm
< pullup resistor
>
GPIO --------+----\
OR------ CS_DAC
SPI_CS -----------/
on boot the gpio is set to high impedance (input) so the pullup resistor makes
it a 1. As the system accesses EEPROM it will toggle SPI_CS but your CS_DAC
will remain 1 (unselected). When you decide to use your DAC you bring the
GPIO low, which lets CS_DAC toggle with the SPI_CS. The EEPROM will not
toggle with the SPI_CS because a bit in a CPLD dissables the EE_CS line when
not in use, (in much the same way as this circuit does for the CS_DAC).
Maybe future versions of the board could have multiple user SPI chip selects
coming from the CPLD. (just an idea)
-Curtis.
On February 15, 2006 04:42 pm, Eddie Dawydiuk wrote:
> Hello,
>
> > but then i need to ensure that the EE_CS for the eeprom and the
additional DIO chip select for my DAC are time multiplexed as they select the
respect ics...
> > for this i would need to continuously monitor the EE_CS and select my DAC
using DIO accordingly..
> > now how do to do it..
> > i even don't know what does the EEPROM do and when is it active...
> > please tell me the functionality of the EEPROM and how to take care of
DIO and EE_CS
>
> One can't execute code out of NAND flash so the bootrom is loaded into the
> EEPPROM. The CPU loads the EEPROM into the on-CPU MAC FIFO SRAM and executes
> from there... That code then understands how to get the rest of the board up
> from the NAND flash. We also store the ADC calibration values in the EEPROM.
>
> So the only time the EEPROM is accessed is at boot time or when a user wants
> to retrieve a calibration value for the ADC.
>
> //Eddie
>
> > Eddie Dawydiuk <> wrote:
> > Hello,
> >
> >> the additional device that i am connecting also has a low chip select
like the EEPROM on the board.
> >>
> >> so how should i take care of it
> >> also there is no SPI chip select signal, so what chip signal are u
talking about..
> >> the EEPROM uses EE_CS...
> >
> > Use a DIO pin as your chip select...
> >
> > //Eddie
> >
> >
> >
> >> Eddie Dawydiuk <> wrote: Hello,
> >>
> >>> The EEPROM is connected to the processor through the SPI interface..
> >>> The same SPI is also available at the DIO portÃÂÂ
> >>> How do I ensure that if I connect a device at the SPI interface at the
DIO port, it doenÃÂÂt affect the functioning of EEPROM..
> >>
> >> That is what the chip select is for, assert the chip select for the
device you
> >> want to communicate with before transfering data to it. Then deassert the
> >> chip select when you have transfered the data...
> >>
> >> //Eddie
> >>
> >>
> >>
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