Re: Help needed with spi interfacing to mcp3208 and ads7871

On 5/1/2013 2:51 PM, santogiuseppe wrote:
> Hello,
> so far i succeeded to interface the minicore 6750 (and the rcm4000) with max4820, max31865 (an RTD-to-Digital Converter) and a touchscreen display but i have serious problems with ads7871 and mcp3208
> I dont know what's the problem, the spi's signals (cs, miso, mosi and the serial clock) are connected to a logic analyzer,
> and the communication (cs, clock and the mosi from the minicore) seems ok, but i'm not receiving the chips replies!!(and i'm going MAD!!)
> I use the same spi with other chips, and i changed the cs only to connect these chips
> Maybe it's the schematics...there is someone who succeeded to interface with the ads787x or mcp320x chips family and is so kind to share the schematics?
> Thanks in advance

I have used the MCP3208. Here is the code:

unsigned read_atod(int chan)
{
    unsigned txbits,rxbits;
    txbits=0x01;    // start bit
    outi(PEDR,srPEDR&=~PORTE_ADCS);
    SPIWrite(&txbits,1);
    txbits=0x80 | (chan<<4);
    SPIWrRd(&txbits,&rxbits,2);
    outi(PEDR,srPEDR|=PORTE_ADCS);
    return swapb(rxbits);
}

This was for Softools, outi() is similar to WrPortI(), it just sets the
CS line low/high. The function swapb() swaps the high/low bytes as they
are received, high/low and I need low/high.

You also need to consider if the SPI library is sending data MSB first
or not. That is determined if SPI_NOREV is defined.

-- 
------------------------------------------
     Scott G. Henion, Consultant
Web site:    http://SHDesigns.org
------------------------------------------