Hardware SPI with BoostC weirdness - Electronic Circuits Projects Diagrams Free

futz · 23rd July 2008, 06:57 AM

EDIT: Never mind! I thought about it some more and realized I had my clock polarity wrong. Changed it and she works perfect!

I wrote this little function to send a byte out the SPI, copying the way I used to do it in assembler (which worked fine).

Code:

void spi_out(unsigned char digit)
{
	unsigned char junk;
	sspbuf=digit;
	while(!sspstat.BF);
	junk=sspbuf;
}

But it doesn't work. The byte in the receiving shift register appears to be shifted by one bit, and of course my 7-seg displays junk. If I remove the sspstat.BF test, it displays correctly, but doesn't work right (hard to explain).

The generated assembly code looks fine:

Code:

52:                void spi_out(unsigned char digit)
53:                {
54:                	unsigned char junk;
55:                	sspbuf=digit;
  008A    501F     MOVF 0x1f, W, ACCESS
  008C    6EC9     MOVWF 0xfc9, ACCESS
56:                	while(!sspstat.BF);
  008E    A0C7     BTFSS 0xfc7, 0, ACCESS
  0090    D7FE     BRA 0x8e
57:                	junk=sspbuf;
  0092    50C9     MOVF 0xfc9, W, ACCESS
  0094    6E20     MOVWF 0x20, ACCESS
58:                }
  0096    0012     RETURN 0

Here's the (working) asm code I ported from:

Code:

spisend	movwf	SSPBUF
	BANKSEL	SSPSTAT
spiloop	btfss	SSPSTAT,BF
	goto	spiloop
	BANKSEL	SSPBUF
	movf	SSPBUF,W
	return

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23rd July 2008, 06:57 AM	#1
futz	Hardware SPI with BoostC weirdness EDIT: Never mind! I thought about it some more and realized I had my clock polarity wrong. Changed it and she works perfect! I wrote this little function to send a byte out the SPI, copying the way I used to do it in assembler (which worked fine). Code: void spi_out(unsigned char digit) { unsigned char junk; sspbuf=digit; while(!sspstat.BF); junk=sspbuf; } But it doesn't work. The byte in the receiving shift register appears to be shifted by one bit, and of course my 7-seg displays junk. If I remove the sspstat.BF test, it displays correctly, but doesn't work right (hard to explain). The generated assembly code looks fine: Code: 52: void spi_out(unsigned char digit) 53: { 54: unsigned char junk; 55: sspbuf=digit; 008A 501F MOVF 0x1f, W, ACCESS 008C 6EC9 MOVWF 0xfc9, ACCESS 56: while(!sspstat.BF); 008E A0C7 BTFSS 0xfc7, 0, ACCESS 0090 D7FE BRA 0x8e 57: junk=sspbuf; 0092 50C9 MOVF 0xfc9, W, ACCESS 0094 6E20 MOVWF 0x20, ACCESS 58: } 0096 0012 RETURN 0 Here's the (working) asm code I ported from: Code: spisend movwf SSPBUF BANKSEL SSPSTAT spiloop btfss SSPSTAT,BF goto spiloop BANKSEL SSPBUF movf SSPBUF,W return __________________ ========================= Futz's Microcontrollers & Robotics ========================= Last edited by futz; 23rd July 2008 at 07:02 AM.