Re: [Gumstix-users] SPI C-code example

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Hi Steve and Dave,

Thanks for the advice. Even after replacing the Frame signal with the =
ADC
/CS input, I just couldn't get the ADC to work. The *Ref_FIFO just =
returned
int 0 after each sample.

To simplify the troubleshooting procedure (I've got no idea if the =
problem
is due to hardware connection or/and software i.e. addressing the ADC
correctly), I've now placed order for free samples of the LTC1867. =
Anyway I
would need to implement faster sampling ADC eventually.

Just to re-confirm with you a couple of things, although the addressing =
part
looks pretty straightforward on this ADC: Based on the example code =
which
you shared with me for LTC1867, there is no need to initialise the =
various
registers (eg communication, setup, clock, data) for the LTC1867. I just
need to assign the first word that is being sent out to indicate the =
channel
number to sample, single/diff, uni/bipolar and sleep mode and SPI will =
pick
up the sample from the ADC data register for each channel. In your =
example,
you had quoted the eight sequential channels as {0x8400, 0xc400, 0x9400,
0xd400, 0xa400, 0xe400, 0xb400, 0xf400}. And on the hardware, your =
direct
connection to the gumstix is as what you have illustrated in your =
earlier
thread. No additional components needed on the circuitry, and no need to =
run
any other SPI program/driver in parallel.

I'll try this out as soon as I've got the free samples (I'll need to =
find a
SSOP to DIP package adapter as well). Any advice for good soldering on =
these
tiny pins?

I'll update you once I managed to sort it out. Thanks.

Peck

-----Original Message-----
From: gum...@li...
[mailto:gum...@li...] On Behalf Of Steve
Sakoman
Sent: 28 January 2008 15:47
To: General mailing list for gumstix users.
Subject: Re: [Gumstix-users] SPI C-code example

> Do you mean you actually connect the Frame signal (on the gumstix) and =
CS
> together? I've tried to fix the CS signal to low throughout the
measurement
> because I've only got one chip on the SPI bus. Is that what you do for =
the
> LTC1867 to work?

Yes, I connect it like so:

ADC          Gumstix

SDI <---NSSP_TXD
SDO--->NSSP_RXD
SCK<---NSSP_CLK
/CS<---NSSP_FRAME

And Dave, yes of course there is a common ground :-)

I have no idea whether this connection scheme will work for your ADC
-- you should study the data sheet.  For the LTC1867 the CS serves
three functions: selecting the chip, framing the serial transfer, and
initiating the next sample/convert operation.  I would imagine that
your ADC functions in a simialr manner, but you should verify by
reading the data sheet.  I don't see how your chip could possibly work
with CS grounded, because there is no facility for framing the serial
transfers.

Steve

On Jan 28, 2008 6:40 AM, Peck Hui Koh <pk...@me...> wrote:
> Hi Steve,
>
> Do you mean you actually connect the Frame signal (on the gumstix) and =
CS
> together? I've tried to fix the CS signal to low throughout the
measurement
> because I've only got one chip on the SPI bus. Is that what you do for =
the
> LTC1867 to work?
>
> Can I ask if you mind sharing with me your schematic (only on the
> gumstix-ADC) as I'm really interested to know how you are able to read =
the
> samples by using the same program, and it will point to us if it's a
> hardware problem.
>
> Your help will be greatly appreciated. Thanks!
>
> Peck
>
> -----Original Message-----
> From: gum...@li...
> [mailto:gum...@li...] On Behalf Of =
Steve
> Sakoman
>
> Sent: 28 January 2008 14:23
> To: General mailing list for gumstix users.
> Subject: Re: [Gumstix-users] SPI C-code example
>
> > On the hardware bits, do we need to have pull-up resistors for the =
data
> > lines (like in i2c bus)? Other than the decoupling capacitors, I've
> directly
> > connected the SCLK, MOSI, MISO to the ADC and having hardwired the =
CS to
> > logic 0 via the GPIO. The Frame line is unused. Am I missing =
something?
>
> Yes, I think you have a hw issue.  You probably need to connect the CS
> to the Frame signal.  The ADC likely requires that signal to function
> properly.  I know the LTC1867 uses the CS signal to initiate the ADC
> conversion as well as to frame the serial data transfer.
>
> No pullups required, though if you are running the ADC at a different
> supply voltage you may want to make sure you don't need to do any
> level conversions.
>
> Steve
>
> On Jan 28, 2008 4:05 AM, Peck Hui Koh <pk...@me...> wrote:
> > Thanks Dave, Steve for your great help.
> >
> > Dave - I've taken your advice and modified the PXm_map and CR_map.
> However,
> > the data output remains saturated as:
> >
> > Transmit OK
> > 0x0000(0xffff)
> > Transmit OK
> > 0x0001(0xffff)
> > Transmit OK
> > 0x0002(0xffff)
> >
> > Do you need to run any other program to enable the SPI bus?
> >
> >
> > Steve - I tried running using your example on my ADC (AD7706). =
However,
> > there seems to have no data output on the screen this time. I did =
some
> > slight changes to read the actual values on one channel (I've copied =
the
> > main program as below while the rest remained unchanged as in your
> example).
> > I realised that the LTC1867 does not require any initialisation (the
first
> > word being sent out indicates which channel to sample). With or =
without
> the
> > initialisation process, I could not retrieve any data from the SPI =
bus.
Am
> I
> > doing something wrong here?
> >
> >
> > On the hardware bits, do we need to have pull-up resistors for the =
data
> > lines (like in i2c bus)? Other than the decoupling capacitors, I've
> directly
> > connected the SCLK, MOSI, MISO to the ADC and having hardwired the =
CS to
> > logic 0 via the GPIO. The Frame line is unused. Am I missing =
something?
> >
> >
> > Too bad I do not have a logic analyser which will then allow me to
> > investigate the data flow. Observing the SCLK via a scope, I'm able =
to
see
> > the oscillation. Any advice will be greatly appreciated.
> >
> > Peck
> >
> >
> > // ---------------------------------------Main Program
> ---------------------
> > int main(int argc, char *argv[])
> > {
> >         int i,j;
> >
> >         long data[16][1];
> >
> >         int ClockDivider =3D 0;
> >
> >         int delay =3D 5;
> >
> >         int channel[] =3D {0x38};
> >
> >         int result =3D SPIinit(ClockDivider);     // Initialize NSSP =
/ SPI
> > Port
> >
> >         int count =3D 10;
> >
> >           for (i=3D0; i < 1; i++) {
> >                 SPI_TxRx(channel[i]); // request channel i data, =
discard
> > result
> >                 usleep(delay);
> >             for (j=3D0; j < count; j++) {
> >                 data[j][i]=3DSPI_TxRx(channel[i]);
> >                 usleep(delay);
> >                 }
> >         }
> >         return 1;
> >
> >         for (i=3D0; i < count; i++) {
> >         printf("%ld\t\n", data[i][0]);
> >         }
> >
> >         fflush(stdout);
> >
> >         close(gpio_fd);
> >
> >   return 1;
> > }
> >
> >
> > -----Original Message-----
> > From: gum...@li...
> > [mailto:gum...@li...] On Behalf Of =
Steve
> > Sakoman
> > Sent: 25 January 2008 15:30
> > To: General mailing list for gumstix users.
> > Subject: Re: [Gumstix-users] SPI C-code example
> >
> > Peck,
> >
> > Here's a quick & dirty command line program to get data from a =
LTC1867
> > 8 channel 16 bit A/D over spi using a user mode program.
> >
> > It samples all 8 channels 4 times each, averages them and prints the
> > averages on the console.
> >
> > I tested it on a connex 200.
> >
> > Steve
> >
> >
> >
> >
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