ADC128D818: AD128D818

Hi Jayashree,

Welcome to our e2e forum!  When you say you are sampling a negative voltage, are you level shifting that before getting to the ADC128D818?  I ask because the ADC128D818 does not accept negative input voltage levels, the normal input range is 0 - 2.56V.  The Limit Registers are fixed at 8-bits (see Table 3, page 19), using the calculation that Joseph noted in the 'Original Question' post - Voltage limit = (ADC code)(Vref)/2^8.  The assumption here is that you've calculated the ADC code related to the input value you want to use as the high/low level limit.  

Hi Tom

Thank you for the response

What is the ADC code?

Suppose my max limit is 2.07V

I would calculate the limit to be stored in registers as

(2.07/0.625)*1000=3312 = CF0 in hex

Correct me if I am wrong

Hi Tim

Can u elaborate the above answer for me

How did you arrive at factor 0.01004?

The same way you did for the LSB size of the conversion.  The ADC128D818 is a 12-bit ADC, so with a 2.56V reference your LSB size is 625 uV/code (2.56 V/4096 codes).  The limit register is only 8-bit, so you need to divide the reference by 256 instead of 4096.  2.56 V/256 codes = 10.04 mV/code.