LTC2480CDD datasheet(38/40 Pages) LINER

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LTC2480

2480f

APPLICATIO S I FOR ATIO

/*** read_LTC2480() ************************************************************

This is the function that actually does all the work of talking to the LTC2480.

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 LTC2480’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_LTC2480(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 LTC2480 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 LTC2480 SPI interface

// Clear configuration bits and subtract offset. This results in

// a 2’s complement 32 bit integer with the LTC2480’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_LTC2480()

LTC2480CDD Datasheet(PDF) 38 Page - Linear Technology

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