• State TI Thinks Resolved
  • Locked Locked
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 46 subscribers
  • Views 246 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADC128D818: ADC128D818

René BRUNIER
Prodigy 30 points
Part Number: ADC128D818

 Hello,

From the datasheet I understand that High Limit / Low Limit registers (2Ah -> 39h) have to be set.

My intent is to use each channel separately (no differential) in Mode 0 (7 user channels +  internal temperature).

Internal VRef will be used (2.56V).

For each user channel, voltage limits should be set to:

  • Low Limit = 0V
  • High Limit =2.5V

What value should I store into high limit registers ?

  • Are the registers 8 signed bytes (so values from -128 to +127, ie -1.28V to +1.27V). if so, how to set to 2.55V ?
  • Are the registers unsigned bytes (so values from 0 to 255, ie 0V to 2.55V). if so how to set a higher value if the voltage ref is, for instance, 5V ?

Can you help understanding how to set these registers ?

Thanks

  • 0
    TI__Genius 15420 points

    Hi René,

    The value going into the register would be an 8-bit unsigned integer, containing the 8 MSBs of your desired voltage limit as an ADC code. Since the limit registers are 8 bits wide, and the ADC128D818 is 12-bit, the limits are practically lower resolution than the ADC by a factor of 16 (2^12/2^8). 

    To get the value that you would be storing in your registers is just like a regular conversion from Vin to an ADC code. ADC Code = 2^n*(Vin/Vref)-1. 

    If you want a 2.5V high limit with the 2.56V internal reference, you would evaluate 2^8*(2.5/2.56)-1. This gives you 250, which is FAh. 

    If you want to simply stop an interrupt from coming out, you would set the low limit to 00h and the high limit to FFh, so that no input voltage would go higher or lower than your limits.

    Best,
    Joel