Cirrus-logic AN74 Instrukcja Użytkownika Pobierz pdf (Strona 10)

AN74

10 AN74Rev2

;****************************************************************

;* Routine - RECEIVE_BYTE

;* Input - none

;* Output - Byte received is placed in R7

;* Description - This routine moves 1 byte from the CS5525/6/9 to the 80C51.

; It transfers the byte by acquiring the logic level on PORT1 BIT 2

; It then pulses SCLK high and then back low again

; to advance the A/D’s serial output shift register to the next bit.

; It does this eight times to acquire one complete byte.

; This function’s prototype in C is: char receive_byte(void);

;Note: This routine can be used three time consecutively to transfer all 24 bits

; from the internal registers of the CS5525/6/9.

;****************************************************************

$DEBUG

USING 0 ; Use register bank 0

TCOD SEGMENT CODE ; Define ROUT as a segment of code

PUBLIC RECEIVE_BYTE ; Make subroutine global

RSEG TCOD ; Make code relocatable

RECEIVE_BYTE:

MOV R1,#08 ; Set count to 8 to receive byte

LOOP: ; Receive the byte

MOV C,P1.2 ; Move bit to carry

RLC A ; Rotate A in preparation for next bit

SETB P1.3 ; Set SCLK

CLR P1.3 ; Clear SCLK

DJNZ R1,LOOP ; Decrement byte, repeat loop if not zero

MOV R7,A ; Byte to be return is placed in R7

RET ; Exit subroutine

END

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Cirrus-logic AN74 Instrukcja Użytkownika Strona 10