16F630 and MCP3221 I2C

[badcock]

Hi,

Has anyone tried interfacing to the MCP3221 ADC via I2C ?

I have the PicKit1 and the MCP3221 Pictail board that puts a direct connection between the RC0, RC1 and SCA SCL. I wanted to test out PicBasic I2C routines linking the 16F630 to the MCP3221.

Problem is that I do not seem to be getting any reading from the ADC. Can anyone suggest where I have gone wrong:

include "modedefs.bas"

' PIC Defines
' -----------

@ __config _INTRC_OSC_NOCLKOUT & _WDT_ON & _PWRTE_ON & _MCLRE_OFF & _BODEN & _CP_OFF & _CPD_OFF 

' PIC16F630 
' PIN NAME USE/CONNECTION
' 1  Vdd  +5VDC
' 2  RA.5 NC
' 3  RA.4 NC
' 4  RA.3 NC
' 5  RC.5 NC
' 6  RC.4 NC
' 7  RC.3 NC
' 8  RC.2 NC
' 9  RC.1 SCL
' 10 RC.0 SCA
' 11 RA.2 NC
' 12 RA.1 LED1 K, LED2 A
' 13 RA.0 LED1 A, LED2 K
' 14 Vss GND

Define OSCCAL_1K 1 	' Set OSCCAL for 1K
DEFINE OSC 4		' 4 MHz OSC


CMCON       =     7        ' PortA = digital I/O
VRCON       =     0        ' Voltage reference disabled
TRISA       =     %00000000' PortA.0-4 = outputs
TRISC       =     %00000001' PortC.1-5 = outputs PORTC.0 = input

SDA var PORTC.0
SCL var PORTC.1

B0      var     byte
B1      var     byte
B2      var     byte
cont con %10011011
loop:
   
    I2CREAD SDA,SCL,cont,[B1,B2]        'Read 2 locations in a row
if B1 > 2 then
	HIGH PORTA.1
	LOW PORTA.2
ELSE
	LOW PORTA.1
	HIGH PORTA.2
Endif

PAUSE 500
        Goto loop  ' Go back to loop and blink LED forever
        End

'goto loop

Thanks,

Rod

[Darrel Taylor]

badcock,

The datasheet for the MCP3221 is a bit ambiguous. While the graphic in figure 5-2 shows the device code as 1001. The text in section 5.2 says that it's 1010.

I've never used that part before, so I don't know which one it really is, but you might try ...

cont con %10101010

Also, the first byte sent (B1) is the highbyte. So the A/D value will have to be greater than 1280 (1.56V) to satisfy the B1 > 2 condition.

And, don't forget the pull-up resistors on SDA and SCL.<br><br>

[badcock]

The datasheet for the MCP3221 is a bit ambiguous. While the graphic in figure 5-2 shows the device code as 1001. The text in section 5.2 says that it's 1010.

Tell me about the ambiguity! One of the reasons I aksed the question is that the AppNote (AN845) and the datasheet are confusing. My problems could stem from this.

I've never used that part before, so I don't know which one it really is, but you might try ...

cont con %10101010

I'll give a few of these variants a go - worth a try for a small amount of effort.

Also, the first byte sent (B1) is the highbyte. So the A/D value will have to be greater than 1280 (1.56V) to satisfy the B1 > 2 condition.

Exactly as it is meant to - I have a pot and reference voltage attached; I should be able to swap the lit LED by turning the pot (nice easy check).

And, don't forget the pull-up resistors on SDA and SCL.<br><br>

Already fitted on the Pictail board - one of the advantages of using two of the Microchip development boards together is that the hardware is definitely correct - pity their software data is so ambiguous!

Many thanks Darrel - I was starting to question whether I had missed some other device specific code. It's nice to have some confirmation that it ma only be the address / control code. Can anyone else confirm the correct MCP3221 control/address byte?

Rod

[badcock]

I just tracked some information down on the Microchip website:

Description: Section 5.2 of the datasheet states '1010' is the 4-bit device code.
However, all of the diagrams indicate '1001' is the device code.
Which is it?

Resolution: The paragraph is incorrect.
The device code is '1001' as stated in the diagrams.

I'll give the other code a try!

Rod

[badcock]

I just tracked some information down on the Microchip website:


I'll give the other code a try!

Rod

But the code I had originally used was correct - could there be something else I am missing?

Rod

[Darrel Taylor]

Rod,

Your comments show that the LED's are on PORTA.0 and PORTA.1

But, PORTA.1 and PORTA.2 are being toggled after reading the ADC<br><br>