MCP3301 A/D converter SPI reading

[flotulopex]

Hi there,

I'm trying to read a 13 bits MCP3301 A/D converter who's output value should go from 0 to 8191.

Unfortunately, even if I can read something, it looks to be only the "upper half" of the expected full value.






Could I have a hardware (wiring) issue or is there something in my code that would be wrong?

' ====== DESCRIPTION ===============================================================================
' MCP3301: SPI 13Bits ADC

' ====== FUSES =====================================================================================
' PIC 16F690 Fuses - Internal oscillator (activate OSCCON register)

'@ __config _FCMEN_OFF &_IESO_OFF &_CPD_OFF &_WDT_OFF &_INTRC_OSC_NOCLKOUT &_BOR_OFF &_CP_OFF &_PWRTE_OFF &_MCLRE_OFF

#CONFIG
    __config _FCMEN_OFF &_IESO_OFF &_CPD_OFF &_WDT_OFF &_INTRC_OSC_NOCLKOUT &_BOR_OFF &_CP_OFF &_PWRTE_OFF &_MCLRE_OFF
#ENDCONFIG

@ ERRORLEVEL -306
@ ERRORLEVEL -202

' ====== REGISTERS =================================================================================
'             76543210
OPTION_REG = %10000000 'PORT A&B Pull-Ups disabled (see WPUA & WPUB)
OSCCON     = %01100000 'Internal RC set to 4MHZ
ANSEL      = %00010100 'Select analog inputs Channels 0 to 7 (AN2 + AN4 selected)
ANSELH     = %00000000 'Select analog inputs Channels 8 to 11
ADCON0     = %10000000 'A/D Module (Bit5:2 select channels 0:11)
ADCON1     = %00000000 'A/D control register
CM1CON0    = %00000000 'Comparator1 Module is OFF
CM2CON0    = %00000000 'Comparator2 Module is OFF
INTCON     = %00000000 'INTerrupts CONtrol (TMR0 OFF)
TRISA      = %00000100 'Set Input/Output (0 to 5)
PORTA      = %00000000 'Ports High/Low (0 to 5)
TRISB      = %00000000 'Set Input/Output (4 to 7)
PORTB      = %00000000 'Ports High/Low (4 to 7)
TRISC      = %00000001 'Set Input/Output (0 to 7)
PORTC      = %00000000 'Ports High/Low (0 to 7)

' ====== DEFINES ===================================================================================
DEFINE OSC 4
DEFINE NO_CLRWDT 1   'Don't waste cycles clearing WDT  
DEFINE HSER_CLOERR 1 'Automatic clear overrun error 
DEFINE SHIFT_PAUSEUS 100

' ====== VARIABLES =================================================================================
SD          var PORTB.4 'SPI Data pin
CS          var PORTB.5 'SPI Chip Select
SCK         var PORTB.6 'SPI Clock pin
Serial_Out  VAR PORTB.7
Mode        Var WORD
MCP3301     Var WORD

' ====== INITIALIZE VARIABLES ======================================================================
CS          = 1
Mode        = 84 'serial com
MCP3301     = 0

' ====== PROGRAM ===================================================================================
MAIN:

    CS = 0                          'initiate 3301 comm
    SHIFTIN SD,SCK,1,[MCP3301\13]   'shift 13 bits of data in, lowest bit first
    CS = 1                          'stop 3301 comm
    
    Serout2 Serial_Out,Mode,["MCP3301: ", BIN13 MCP3301," - ", DEC4 MCP3301,13,10]
    
    PAUSE 1000

    GOTO MAIN
END

[richard]

according to the data sheet the data read is 12 data bits + sign bit

[flotulopex]

Really?



I don't get it

[richard]

i'm looking at the data sheet you posted, that's what i see

[tumbleweed]

Keep reading. It's a 13-bit differential converter.

From the datasheet section 5.1:

and the device uses the collected charge to produce a serial 13-bit binary two’s complement output code.

So that's 12 bits of data + sign. See Section 6.1.

[flotulopex]

Okay then, didn't see that one 😵

So I'll get a 12 bits "value" and the last bit will indicate either "+" or "-", right?

[richard]

the last bit will indicate either "+" or "-", right?

if by last bit you mean the msb then yes
not forgetting its a 13-bit binary two’s complement number

[flotulopex]

not forgetting its a 13-bit binary two’s complement number

...and that means what exactly please?