I2C Comm with Digital Compass HMC6352

[jihlein]

This is my first post to the group.

I'm designing a heading hold autopilot for a free flight glider. I'm basing it on a PIC16F88, and using an HMC6352 digital compass (http://www.sparkfun.com/datasheets/C...ts/HMC6352.pdf).

I've never played with I2C before, and figured that I would try something simple first, like reading an EEPROM register in the compass module. My problem is that no matter what I do, I seem to always read back a value that is exactly 1/2 of what it should be.

So then I tried writting a value to a RAM address and reading it back. Again, same issue, the value read back is 1/2 the value written.

I'm using PIC BASIC PRO, on a LABX18 development board. Here's the code I'm using for the EEPROM read, which is modified from some of the example programs:

Define  LCD_DREG        PORTA
Define  LCD_DBIT        0
Define  LCD_RSREG       PORTB
Define  LCD_RSBIT       6
Define  LCD_EREG        PORTB
Define  LCD_EBIT        3

' Define I2C Interface

SDA    Var    PORTB.1                    ' Data pin
SCL    Var    PORTB.4                    ' Clock pin

cmd  Var Byte
addr Var Byte
cont Var Byte

    ANSEL = 0                      ' PORTA is digital
    CMCON = 7                      ' PORTA is digital

    Pause 100                    ' Wait for LCD to start up
        
loop1:
    pauseus 1000
    cmd = $72                    ' Read from compass EEPROM
    addr= $00                    ' EPROM address $00
    I2CWRITE SDA, SCL, $42, [cmd, addr], nowrite

    pauseus 1000
     I2CREAD SDA, SCL, $42, [cont], noread
    Lcdout $fe, 1, "Data: ", cont
    
    goto loop1
    
    End

nowrite:
    Lcdout $fe, 1, "Write Err"
    goto nowrite

noread:
    Lcdout $fe, 1, "Read Err"
    goto noread

If anyone can point me to the error of my ways, it would be greatly appreciated.

John Ihlein
Albuqueruqe, NM