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fix ads7843 data fetching 

The old code forgot to drop the MSB in the very first byte retrieved from ads7843 after a control byte. This will lead to data corruption especially in 16-Clocks per conversion mode.

git-svn-id: https://rt-thread.googlecode.com/svn/trunk@1781 bbd45198-f89e-11dd-88c7-29a3b14d5316
This commit is contained in:
chaos.proton@gmail.com 2011-11-02 08:17:40 +00:00
parent 4f62f6e568
commit 9de3512c8a
1 changed files with 13 additions and 5 deletions
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18
bsp/stm32f10x/touch.c
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@ -92,14 +92,22 @@ static void rtgui_touch_calculate()
rt_uint16_t tmpy[10];
unsigned int i;
/* From the datasheet:
* When the very first CLK after the control byte comes in, the
* DOUT of ADS7843 is not valid. So we could only get 7bits from
* the first SPI_WriteByte. And the got the following 5 bits from
* another SPI_WriteByte.(aligned MSB)
*/
for(i=0; i<10; i++)
{
CS_0();
WriteDataTo7843(TOUCH_MSR_X); /* read X */
tmpx[i] = SPI_WriteByte(0x00)<<4; /* read MSB bit[11:8] */
tmpx[i] |= ((SPI_WriteByte(TOUCH_MSR_Y)>>4)&0x0F ); /* read LSB bit[7:0] */
tmpy[i] = SPI_WriteByte(0x00)<<4; /* read MSB bit[11:8] */
tmpy[i] |= ((SPI_WriteByte(0x00)>>4)&0x0F ); /* read LSB bit[7:0] */
WriteDataTo7843(TOUCH_MSR_X);
tmpx[i] = (SPI_WriteByte(0x00) & 0x7F) << 5;
tmpx[i] |= (SPI_WriteByte(TOUCH_MSR_Y) >> 3) & 0x1F;
tmpy[i] = (SPI_WriteByte(0x00) & 0x7F) << 5;
tmpy[i] |= (SPI_WriteByte(0x00) >> 3) & 0x1F;
WriteDataTo7843( 1<<7 ); /* 打开中断 */
CS_1();
}