An74 – Cirrus Logic AN74 User Manual
Page 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