1993_Motorola_Linear_Interface_ICs_Vol_2.pdf

SPI TRANSFER LOOP
MC33298
;Set the number of Read/Shift cycles.
LOOP ASL DATAIN ;Shift a Zero into LSB of DATAIN and ASL other bits.
ASL DTOUT ;Test value currently in MSB of DTOUT.
BCS DOONE ;
BCLR 7,PORTA ;MSB was Zero, so clear DATA OUT bit.
JMP GOON
DOONE BSET 7,PORTA ;MSB was One, so set the DATA OUT bit.
GOON BSET 6,PORTA ;Set the SCLK. Serial Output pin of the MC33298 changes state on the rising edge of the SCLK.
Read the next bit coming from the MC33298.
BRCLR O,PORTA, ;Read the bit and branch if Zero. LSB of DATAIN is already cleared due to the ASL above.
WZZERO
BSET O,DATAIN ;Bit was One. Set the next bit in DATAIN.
WZZERO BCLR 6,PORTA ;Clear SCLK. Falling edge causes the MC33298 to read the next bit from the MCU.
DECX
ESTABLISH A BRIEF DELAY
BPL LOOP ;Continue to loop eight times until the SPI transfer is complete.
LOA #16
PAUSE DECA ;3 Clock cycles
BNE PAUSE ;3 Clock cycles
;Transfer control signal to output transistors.
BCLR 5,PORTA ;Transfer output status to Serial Register.
JSR FLTCHK ;Jump to Fault Check subroutine.
JSR DLY ;Delay 11T msec
SUBROUTINE TO CHECK FOR FAULTS
FLTCHK BCLR
LDA
CMP
BEQ
BSET
NOFLT RTS
;Deselect the MC33298.
;Return to top of loop.
1 ,PORTA ;CLR the Fault pin.
DATAIN
VALUE ;Check for Faults.
NOFLT ;If there is no Fault, continue.
1,PORTA ;Activate Fault LED.
MOTOROLA LINEAR/INTERFACE ICs DEVICE DATA
10-97
IDI I