Compass module and I2C bus

[vladimir059@hot]

Hello everybody. I bought compass module CMPS03 produced by Devantech. It’s employs I2C bus. I wrote a program but it doesn’t work properly. I expect readings from 0 to 359 but I have from 65535 to 49279 and readings are jumping. I’m novice in I2C bus technology, and I can’t figure out what is the problem. If someone has experience with this module, please let me know where I made a mistake or at least point me on a good tutorial of I2C bus.
Thank you in advance
Vladimir

This is my code
'---------------- Definitions---------------------------------------------
define OSC 20
'------------- Define LCD registers and bits------------------------------
Define LCD_DREG PORTB 'Set LCD data port
Define LCD_DBIT 0 'Set starting data bit
Define LCD_RSREG PORTB 'Set LCD register select port
Define LCD_RSBIT 4 'Set LCD register select bit
Define LCD_EREG PORTB 'Set LCD enable port
Define LCD_EBIT 5 'Set LCD enable bit
define DEBUG_REG PORTC
DEFINE DEBUG_BIT 3
DEFINE DEBUG_BAUD 2400
DEFINE DEBUG_MODE 0



DPIN var PORTc.2 ' I2C data pin
CPIN var PORTc.1 ' I2C clock pin
bearing var word


Main
i2cread dpin,cpin,%11000000,1,[bearing]
lcdout $fe, 1,"Bearing ", # bearing
DEBUG " Compass Bearing ",DEC bearing,13,10

pause 200

goto main

[mister_e]

Have a look at this one for Basic Stamp
http://www.robot-electronics.co.uk/htm/cmps2bs2.shtml
http://www.robot-electronics.co.uk/htm/cmpsatom.shtml

I don't think your software is the main problem.. double check your hardware first

And probably you need to calibrate it first...
http://www.robot-electronics.co.uk/htm/cmps_cal.shtml

EDIT: AHHHH F*** You used a Word sized Variable... it must be a BYTE sized variable for this specific register

[vladimir059@hot]

Hello Mister E.
I tried everything, but it doesn’t work.
I contacted to Devantech Co and Gerald said:
“We've had this before.
It's the PIC Basic Pro compiler.
It does not correctly implement the I2C bus protocol (SCL bus hold).”

Maybe exist other way to implement I2C protocol, or some sort of trick which can help me to overcome these limits
Vladimir

[mister_e]

mpffffff well if it works with a Stamp.. and i use I2CREAD/WRITE in 90% of my stuff without problem, i would probably look at something else first before to tell it's a compiler related stuff.

Tell us your PIC model

Post your config fuses settings

post your schematic

Once again, i doubt it's a PBP problem...

[mister_e]

what happened to your results when you change to a Byte Sized variable? you should read something between 0-255

NOW if you want to use a word sized variable, YOU MUST READ register #2, not 1, so try...

ControlByte VAR BYTE
Register VAR BYTE
ControlByte = $C0
Register = 2
'
'
'
'
i2cread dpin,cpin,ControlByte,Register,[bearing.highbyte, bearing.lowbyte]

and you should read something in a range of 0-3599
<img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=1249&stc=1&d=116582183 1">

About now?

[vladimir059@hot]

Big Thank You Mister E.
You and MELABs staff helped me to find mistake. I insert in my code two lines and now program works great. These are two lines:
DEFINE I2C_HOLD 1
DEFINE I2C_SLOW 1

Maybe, someone will have the same problems in future, so I decided to post all my code. It works flawless.
Thanks again
Vladimir

'PIC16f872
'---------------- Definitions---------------------------------------------
define OSC 20
'------------- Define LCD registers and bits------------------------------
DEFINE I2C_HOLD 1
define I2C_SLOW 1
Define LCD_DREG PORTB 'Set LCD data port
Define LCD_DBIT 0 'Set starting data bit
Define LCD_RSREG PORTB 'Set LCD register select port
Define LCD_RSBIT 4 'Set LCD register select bit
Define LCD_EREG PORTB 'Set LCD enable port
Define LCD_EBIT 5 'Set LCD enable bit
define DEBUG_REG PORTC 'Set DEBUD port
DEFINE DEBUG_BIT 1 'Set DEBUG pin
DEFINE DEBUG_BAUD 2400 'Set DEBUG baud rate
DEFINE DEBUG_MODE 0 'Set DEBUG mode



DPIN var PORTc.4 ' I2C data pin
CPIN var PORTc.3 ' I2C clock pin
bearing var word ' word size bearing value 0 - 359
bearing1 var byte ' byte size bearing value 0 - 255

Main:
i2cread dpin,cpin,%11000000,2,[bearing.Highbyte,bearing.lowbyte]

lcdout $fe, 1,"BEARING ",DEC BEARING/10

i2cread dpin,cpin,%11000000,1,[bearing1]

lcdout $fe, $c0,"Bearing ", dec bearing1

DEBUG " Compass Bearing ", # bearing,13,10

pause 20

goto main

[mister_e]

Nice!

Now forward the info to Devantech