SPI: PIC18f4550 - MCP3201 ADC

[asp87]

Hi,

I'm trying to communicate with **broken link removed**(12 bit ADC) through SPI using PIC18f4550.
MCP3201 should start A to D conversion once the chip_select goes low. After 1.5 clocks, it'll finish sampling and send out the digital data MSB first.

My problem:

The code runs till the label "start_conversion" but not after that. I know this from the status of two LEDs, the commands for which are written before and after the start_conversion label. Can you please look into the code and tell where I'm going wrong?

In SPI protocol, when does the PIC start transmitting clock signal? Right after configuring or do we need to do something for it to start transmission? I measured the voltage at PIC RB1 pin (SCLK). It's 0V. Does it mean there is no clock signal?

 LIST P=18F4550        ;directive to define processor    
     #include <P18F4550.INC>    ;processor specific variable definitions    
         
     cblock 0x20    
     d1    
     d2    
     d3     
     RxData    
     endc    
         
     CONFIG    FOSC=HS                    ; HS oscillator, HS used by USB    
     CONFIG    PWRT=ON                    ; Power on timer    
     CONFIG    BOR=OFF                    ; Brown out off    
     CONFIG    WDT=OFF                    ; Watch dog off    
     CONFIG    PBADEN=OFF                ; Port B en digital IO    
     CONFIG    LVP=OFF                    ; Pas de prog single supply    
     CONFIG    ICPRT=OFF                ; Port de debug off    
     CONFIG    DEBUG=OFF                ; Debug off    
         
     org    0x00    
     goto    main    
 
     org    0x10    
         
 main    
     bcf INTCON, GIE    
     movlw b'10000000' ; Fosc/64    
     movwf SSPSTAT    
     movlw 0x22 ; 0001 0110    
     movwf SSPCON1    
         
     movlw 0x00    
     movwf    LATB    
     movwf    LATC    
     movwf    LATD    
     movwf    TRISC ; RC7 is SDO    
     movwf    TRISD    
     movlw b'00000001'  ; RB0 is SDI, RB1 is SCLK    
     movwf    TRISB    
         
     bsf LATD,2 ; bring chip_select high    
     call Delay    
 
     bcf LATD,2 ; bring chip_select low to start A to D conversion    
     bsf LATD,0 ; Green LED- This LED lights up    
         
 start_conversion    
     btfss SSPSTAT, 0    
     bra start_conversion    
     movf SSPBUF, 0    
     movwf RxData    
         
     bsf LATD,1 ; Red LED - This does not light up    
         
     movlw 0x0A    
     movwf EEADR    
     movlw RxData    
     movwf EEDATA    
     bcf EECON1, EEPGD    
     bcf EECON1, CFGS    
     bsf EECON1, WREN    
     bcf INTCON, GIE    
     movlw 55h    
     movwf EECON2    
     movlw 0AAh    
     movwf EECON2    
     bsf EECON1, WR    
     bcf EECON1, WREN    
         
 loop_1    
     nop    
     bra loop_1    
 
 ;---------------------------------------------------------------------    
         
 Delay                 ;0.5 s, 20MHz             
          movlw    0x01         
          movwf    d1         
          movlw    0x01         
          movwf    d2         
          movlw    0x02         
          movwf    d3         
 Delay_0         
          decfsz    d1, f         
          bra    $+4        
          decfsz    d2, f         
          bra    $+4         
          decfsz    d3, f         
          bra    Delay_0         
          bra    $+2           
          bra    $+2            
          return     
              
  end

**broken link removed**

 

[bsprajc]

start_conversion
btfss SSPSTAT, 0
bra start_conversion
movf SSPBUF, 0
movwf RxData

bsf LATD,1 ; Red LED - This does not light up



Since SPI read/writes at the same time and since your are a SPI master, I think you need to initiate a write so that the master will clock in the read data.

You might want to try writing to SSPBUF before your btfss instruction and modify your polling loop to branch back to the btfss instruction (not the write to SSPBUF which would now be at start_version)

I hope this helps, please let us know if it does.

 

[asp87]

Hi,
I tried doing it for a while but didn't work. Hence proceeded with software SPI.
I'll try going the hardware route in a few days and let you know.

Thanks.