Re: Configuration of MAX7301

[Grant Likely <grant.likely-s3s/WqlpOiPyB63q8FvJNQ@public.gmane.org>]

On Thu, Mar 3, 2011 at 3:57 AM, Vikram Narayanan <vikram186-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> Hi,
>
> I am trying to interface the MAX7301 IC with my Samsung S3C2440 processor.
> The problem is the S3c supports only 8 bit word length for SPI transfer,
> whereas my MAX requires 16 bit word length.

You're talking about spi which at it's heart is just a stream of bits.
 Not 8 bit, not 16 bit.  Just a stream.  The device may make
assumptions about how the stream is framed into 16 bit hunks, and the
spi_master may have limitations on how the data buffer is organized (8
bit bytes), but that does not prevent the two from working together.

What you need to do is arrange the data in the transfer buffer so that
the bits get streamed out in the order expected by the MAX7301.  It's
educational to break out an oscilloscope and experiment with different
transfers so you can get familiar with how the bits appear on the
wire.  Then you'll be able to figure out how to arrange the transfer
so that the device gets what it needs.

I do *not* recommend using the bitbang driver when you've got a proper
spi master at your disposal.

g.

> I couldn't find any info on the datasheet to use the IC on a 8 bit word
> length. can i make the max7301_write function,
>
> static int max7301_write(struct spi_device *spi, unsigned int reg, unsigned
> int val)
> {
>    u8 command = reg & 0x7F;
>    u8 data = val & 0xFF;
>    spi_write(spi, (const u8*)&command, sizeof(command));
>    spi_write(spi, (const u8*)&data, sizeof(data));
>    return 0;
> }
>
> Will this make the IC work? Please share your ideas.
> --
> Regards
> Vikram
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-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.

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