Hi all,
I have a F500DK development kit from SiLabs (https://www.silabs.com/products/mcu/automotive/Pages/C8051F50x-51x.aspx) and I am attempting to communicate with a Honeywell compass module (http://www.ssec.honeywell.com/magnetic/datasheets/hmr32003300.pdf) via SPI. In order to initiate SPI comms, I first pull a pin on the compass module low. Then, the compass sends an 's' and according to the datasheet of the compass, I must immediately send an 'h' to request the current heading. The compass is the Master as it controls the SCK line.

The compass responds to my 'h' by sending the current heading as two bytes.

I have a few versions of code written up but for the life of me, I can't seem to get the proper data. I am new to this chip and SPI so the crossbar and many of its features have presented difficulties while I try to get my feet wet with this chip and SPI.

My current code is below. What is the proper way to initiate SPI communication? What am I missing here? Should I use the SPI interrupt? Are there any "coding for SPI" type tutorials available online? Any help you can offer would be greatly appreciated.

Thanks in advance.

$include (c8051f500.inc)     ;Use C8051F50x predefined symbols

;-------------------------------------------
;Assign names to port pins
PULSE EQU P1.7 
SCK EQU P2.0
MISO EQU P2.1
MOSI EQU P2.2
CS EQU P2.3
;---------------------------------------------------------------------------
CSEG                 ;Define the following as code
ORG 0000h            ;Load code starting at 0000h
JMP MAIN             ;Jump to MAIN
;---------------------------------------------------------------------------
ORG 000bh            ;Timer 0 interrupt subroutine

CLR TR0              ;Stop Timer 0
CLR TF0              ;Clear Timer 0 overflow flag
DEC R2               ;Decrement R0
SETB 00h             ;Set bit located at 00h
RETI                 ;Return from interrupt
;----------------------------------------------------------------------------

ORG 060h             ;Start MAIN outside ISR Space

MAIN: 

MOV SPI0CN, #01h     ;Config SPI
MOV P1MDOUT,#80h     ;Set P1.7 to push-pull
MOV P2MDOUT,#008h    ;Set P2.3 to push-pull
MOV P0SKIP,#0FFh     ;Force crossbar to skip all P0 pins
MOV P1SKIP,#0FFh     ;Force crossbar to skip all P1 pins
MOV P2SKIP,#008h     ;Force crossbar to skip P2.3
MOV XBR0,#04h        ;Enable SPI I/O routing to port pins
MOV XBR2,#40h        ;Enable the Crossbar
SETB EA              ;Enable interrupts
SETB ET0             ;Enable Timer 0 interrupt 

MOV TMOD,#01         ;Put Timer 0 in 16-bit mode
;---------------------------------------------------------------------------
REQUEST:

CLR CS               ;Write a zero to CS pin to initiate SPI comm
MOV SPI0DAT,#'h'     ;Send an 'h' to request the current heading 
JNB TXBMT,$          ;Wait here until the transmit buffer is clear
JNB SPIF,$           ;Wait here until the SPI receive flag goes high
MOV R0,SPI0DAT       ;Move the contents of the SPI receive 
                     ;buffer to R0 (high byte)
CLR SPIF             ;Clear the SPI receive flag
JNB SPIF,$           ;Wait here until another 8 bits have been received
MOV R1, SPI0DAT      ;Move the contents of the SPI receive
                     ;buffer to R1 (low byte)
SETB CS              ;Write a 1 to CS to stop the SPI communication
CLR SPIF             ;Clear the SPI receive flag
MOV R2,25            ;Move a value of 25 to the R2 register

WAIT:

CLR 00h              ;Clear 00h before restarting WAIT loop
MOV TH0,#76          ;Set T0 high byte to 19,456
MOV TL0,#00          ;Set T0 low byte to 0
SETB TR0             ;Turn on Timer 0 to wait for heading data
JNB 00h,$            ;Wait here until 00h is set
CJNE R2,#0h,WAIT     ;Jump back to wait if R0 does not equal 0
                     ;This forces the program to pause
                     ;before requesting another heading
                     ;from the compass
LJMP REQUEST         ;Jump back to request to start heading request 


END