spi.asm

来自「web51的开发库」· 汇编 代码 · 共 45 行

;#########################
;# SPI bus communication #
;#########################
;
.equ	CLK_SPI, 0x91	; P1.1
.equ	DQ_SPI,  0x92	; P1.2

	.text
	.using	0

.global	spiout
.local	spiouLp, spiouEnd
spiout:	; Shift out a byte to the SPI, last significant bit first.
	; CLK, DQ expected high on entry. Return with CLK high.
	; Called with data to send in A.
	; Destroys A.
	setb	C		; stop mark
spiouLp:rrc	a		; move bit into CY
	jz	spiouEnd
	clr	CLK_SPI		; drop clock
	mov	DQ_SPI, C	; output bit
	nop
	setb	CLK_SPI		; raise clock
	clr	C
	sjmp	spiouLp		; next bit
spiouEnd:
	ret

.global	spiin
.local	spiinL	
spiin:	; Shift in a byte from the SPI, last significant bit first.
	; CLK, DQ expected high on entry. Return with CLK high.
	; Returns received data byte in A.
	mov	a,#0x80		; stop marker
	setb	DQ_SPI		; make SPI Data Line an input
spiinL:	clr	CLK_SPI		; drop clock
	nop
	mov	c, DQ_SPI	; input bit
	setb	CLK_SPI		; raise clock
	rrc	a		; move bit into byte
	jnc	spiinL		; next bit
	ret

	;; end