Thus spake Bradley, Larry (Larry.Bradley@NRC.CA):

> Has anyone written code for the MAXIM 186 8-channel serial A/D converter
> (or any of the MAX serial A/Ds? If no-one has, I'll have to, and will

Here is some C code for driving the MAX186 from an XA micro - it should
at least give you a starting point. Make sure you do the timing calculations
to ensure all the parameters are met (should not be a problem with
a PIC). This code uses internal clock mode - using external clock mode
can result in faster throughput, if done properly.


static far unsigned char        ADIN @ 0xF8000;         /* input port */
#define SSTRB   0x01                            /* strobe is bit 1 */
#define DATAIN  0x02                            /* input data bit */

static far unsigned char        ADOUT @ 0xE0000;        /* output port (leds too
 */
#define SSCLK   0x02                            /* output clock bit */
#define DATAOUT 0x01                            /* output data bit */

#define ADCS    T1                              /* T1 selects the ADC */


/* Fuction:     write_word
 * Descrip:     Write one byte to the ADC. The MSB of val must be set.
 * Arguments:
 * Returns:     <none>
 */
static void
write_word(unsigned char val)
{
        unsigned char   i, j;

        ADOUT = SSCLK;          /* set clock high */
        T1 = 0;                 /* select chip */
        i = 8;

        /* the timing of this loop is such that the 1.5uS
           sample and hold time is met in the last 3 bits,
           even at 30MHz processor clock
         */
        do {
                j = (val >> 7) & 0x1;   /* get a bit */
                ADOUT = j;                      /* drive clock low */
                val <<= 1;
                ADOUT = SSCLK | j;              /* clock high */
        } while(--i);
        ADOUT = 0;                              /* set clock low */
        ADCS = 1;                               /* deselect chip */
}


/* Fuction:     read_word
 * Descrip:     Read two bytes from the ADC, deselect CS. It assumes
 *              write_adc has been called to start the conversion.
 * Arguments:   <none>
 * Returns:
 */
static unsigned int
read_word(void)
{
        unsigned char   i;
        unsigned int    val;

        ADCS = 0;                       /* select the chip */
        for(val = 0xFFFF ; --val ; )
                if(ADIN & SSTRB)        /* wait for completion */
                        break;
        if(!(ADIN & SSTRB))             /* timeout? Return impossible value */
                return 0xFFFF;
        val = 0;
        i = 12;                         /* we only need 12 bits */
        do {
                ADOUT = SSCLK;          /* clock high */
                val <<= 1;
                ADOUT = 0;              /* clock low */
                if(ADIN & DATAIN)
                        val |= 1;
        } while(--i);
        ADCS = 1;                       /* deselect chip */
        return val;
}

/* Fuction:     adc
 * Descrip:     Perform a conversion on the specfied channel
 * Arguments:
 * Returns:
 */
unsigned int
adc(unsigned char chan)
{
        write_word((chan << 4) | 0x8E);
        return read_word();
}

--
Clyde Smith-Stubbs    | HI-TECH Software,       | Voice: +61 7 3354 2411
clyde@htsoft.com      | P.O. Box 103, Alderley, | Fax:   +61 7 3354 2422
http://www.htsoft.com | QLD, 4051, AUSTRALIA.   |
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