参数资料
型号: DC939A
厂商: Linear Technology
文件页数: 33/42页
文件大小: 0K
描述: BOARD DELTA SIGMA ADC LTC2484
软件下载: QuikEval System
设计资源: DC939A Design File
DC939A Schematic
标准包装: 1
系列: Easy Drive™, QuikEval™
ADC 的数量: 1
位数: 24
采样率(每秒): 6.8
数据接口: MICROWIRE?,串行,SPI?
工作温度: 0°C ~ 70°C
已用 IC / 零件: LTC2484
已供物品:
相关产品: LTC2484CDD#TRPBF-ND - IC ADC 24BIT 10-DFN
LTC2484IDD#TRPBF-ND - IC ADC 24BIT 10-DFN
LTC2484IDD#PBF-ND - IC ADC 24BIT 10-DFN
LTC2484CDD#PBF-ND - IC ADC 24BIT 10-DFN
LTC2484
39
2484fd
APPLICATIONS INFORMATION
/*** read _ LTC2484() ************************************************************
This is the function that actually does all the work of talking to the LTC2484.
The spi _ read() function performs an 8 bit bidirectional transfer on the SPI bus.
Data changes state on falling clock edges and is valid on rising edges, as
determined by the setup _ spi() line in the initialize() function.
A good starting point when porting to other processors is to write your own
spi _ write function. Note that each processor has its own way of configuring
the SPI port, and different compilers may or may not have built-in functions
for the SPI port. Also, since the state of the LTC2484’s SDO line indicates
when a conversion is complete you need to be able to read the state of this line
through the processor’s serial data input. Most processors will let you read
this pin as if it were a general purpose I/O line, but there may be some that
don’t.
When in doubt, you can always write a “bit bang” function for troubleshooting
purposes.
The “fourbytes” structure allows byte access to the 32 bit return value:
struct fourbytes
// Define structure of four consecutive bytes
{
// To allow byte access to a 32 bit int or float.
int8 te0;
//
int8 te1;
// The make32() function in this compiler will
int8 te2;
// also work, but a union of 4 bytes and a 32 bit int
int8 te3;
// is probably more portable.
};
Also note that the lower 4 bits are the configuration word from the previous
conversion. The 4 LSBs are cleared so that
they don’t affect any subsequent mathematical operations. While you can do a
right shift by 4, there is no point if you are going to convert to floating point
numbers - just adjust your scaling constants appropriately.
*******************************************************************************/
signed int32 read _ LTC2484(char config)
{
union
// adc _ code.bits32
all 32 bits
{
// adc _ code.by.te0
byte 0
signed int32 bits32;
// adc _ code.by.te1
byte 1
struct fourbytes by;
// adc _ code.by.te2
byte 2
} adc _ code;
// adc _ code.by.te3
byte 3
output _ low(CS);
// Enable LTC2484 SPI interface
while(input(PIN _ C4)) {}
// Wait for end of conversion. The longest
// you will ever wait is one whole conversion period
// Now is the time to switch any multiplexers because the conversion is finished
// and you have the whole data output time for things to settle.
adc _ code.by.te3 = 0;
// Set upper byte to zero.
adc _ code.by.te2 = spi _ read(config);
// Read first byte, send config byte
adc _ code.by.te1 = spi _ read(0);
// Read 2nd byte, send speed bit
adc _ code.by.te0 = spi _ read(0);
// Read 3rd byte. ‘0’ argument is necessary
// to act as SPI master!! (compiler
// and processor specific.)
output _ high(CS);
// Disable LTC2484 SPI interface
// Clear configuration bits and subtract offset. This results in
// a 2’s complement 32 bit integer with the LTC2484’s MSB in the 2^20 position
adc _ code.by.te0 = adc _ code.by.te0 & 0xF0;
adc _ code.bits32 = adc _ code.bits32 - 0x00200000;
return adc _ code.bits32;
} // End of read _ LTC2484()
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