/*!
LTC2422: 1-/2-Channel 20-Bit uPower No Latency Delta-Sigma ADC in MSOP-10

@verbatim

The LTC2421/LTC2422 are 1- and 2-channel 2.7V to 5.5V micropower 20-bit analog-
to-digital converters with an integrated oscillator, 8ppm INL and 1.2ppm RMS
noise. These ultrasmall devices use delta-sigma technology and a new digital
filter architecture that settles in a single cycle. This eliminates the latency
found in conventional delta-sigma converters and simplifies multiplexed
applications. Through a single pin, the LTC2421/LTC2422 can be configured for
better than 110dB rejection at 50Hz or 60Hz +/-2%, or can be driven by an
external oscillator for a user defined rejection frequency in the range 1Hz to
120Hz. The internal oscillator requires no external frequency setting
components.

SPI DATA FORMAT (MSB First):

            Byte #1                            Byte #2

Data Out :  !EOC CH SIG EXR D19 D18 D17 D16   D15  D14  D13  D12  D11  D10 D9  D8
Data In  :  X    X   X   X   X   X   X   X     X    X    X    X    X    X   X   X

Byte #3
D7 D6 D5 D4 D3 D2 D1 D0
X  X  X  X  X  X  X  X

!EOC : End of Conversion Bit (Active Low)
CH   : Channel Indicator Bit (0 - CH0 , 1 - CH1)
SIG  : Sign Bit (1-data positive, 0-data negative)
EXR  : Extebded Input Range Indicator Bit
Dx   : Data Bits

Example Code:

Read Channel 0.

    uint16_t miso_timeout = 1000;
    if(LTC2422_EOC_timeout(LTC2422_CS, miso_timeout))        // Check for EOC
        return; // Handle exception if timeout exceeded without EOC
    LTC2422_adc_read(LTC2422_CS, &adc_channel, &adc_code);  // Read ADC

    if(adc_channel != 0)
    {
        if(LTC2422_EOC_timeout(LTC2422_CS, miso_timeout))    // Check for EOC
            return; // Handle exception if timeout exceeded without EOC
        LTC2422_adc_read(LTC2422_CS, &adc_channel, &adc_code); // Reads the ADC again if the first reading was not CH0
    }
    adc_voltage = LTC2422_code_to_voltage(adc_code, LTC2422_lsb);

@endverbatim

http://www.linear.com/product/LTC2422

http://www.linear.com/product/LTC2422#demoboard


Copyright 2018(c) Analog Devices, Inc.

All rights reserved.

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   contributors may be used to endorse or promote products derived
   from this software without specific prior written permission.
 - The use of this software may or may not infringe the patent rights
   of one or more patent holders.  This license does not release you
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THIS SOFTWARE IS PROVIDED BY ANALOG DEVICES "AS IS" AND ANY EXPRESS OR
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*/

/*! @file
    @ingroup LTC2422
    Library Header File for LTC2422: 1-/2-Channel 20-Bit uPower No Latency Delta-Sigma ADC in MSOP-10
*/

#ifndef LTC2422_H
#define LTC2422_H

#include <SPI.h>

//! Define the SPI CS pin
#ifndef LTC2422_CS
#define LTC2422_CS QUIKEVAL_CS
#endif

const float LTC2422_TYPICAL_lsb = 4.7683761E-6; //!< The LTC2422 typical least significant bit value with 5V full-scale

//! Checks for EOC with a specified timeout
//! @return success or failure on timeout
uint8_t LTC2422_EOC_timeout(uint8_t cs,           //!< Chip Select pin
                            uint16_t miso_timeout //!< Timeout (ms)
                           );

//! Read ADC code from the LTC2422. Does not wait for end-of-conversion.
//! To automatically wait for conversion to complete, use the LTC2422_EOC_timeout before this function.
//! @return void
void LTC2422_adc_read(uint8_t cs,           //!< Chip Select pin
                      uint8_t *adc_channel, //!< Returns channel number read.
                      int32_t *code        //!< Returns the ADC code read.
                     );

//! Calculates the voltage given the ADC code and lsb weight.
//! @return calculated voltage (based on ADC code and lsb weight).
float LTC2422_code_to_voltage(int32_t adc_code,    //!< ADC code read from LTC2422.
                              float LTC2422_lsb     //!< LSB weight (determined by reference voltage).
                             );

//! Calculates the lsb weight from the given reference voltage.
//! @return Void
void LTC2422_calculate_lsb(float LTC2422_reference_voltage, //!< Measured reference voltage.
                           float *LTC2422_lsb               //!< Overwritten with the lsb weight in volts.
                          );

#endif  //  LTC2422_H