Dear ADIer

Please help me to understand how to calculate the ADC code.

- I wonder about the meaning of output code. Code 000 ... 000, code 100 ... 000, code 111.111 in the Data Output Coding Session of ADUC845 Datasheet page 36
- I can calculate Code = (2.56V x 1 x 2^16) / (1.024 x 2.56Vref) = 64000(H) = 0110 0100 0000 0000 0000. Is it correct?
- I am wondering about the meaning of input voltage like zero differential, midscale and full scale. What is the reference for this definition in sight of input allowable voltage range
With respect to GAIN, it is 1 at 2.56V range, and it is composed of 20mv units. Should the measured value be larger if Gain is large? If you look at the sample range, it looks like it's shrinking.

On the same page, I want to know about the purpose and IEXC1 / 2.

- Could you explain the Sinc Filter 69 = decimal in figure 18,

Thanks..

Hi,

Answer:The ADC data is 12 bits wide and "Code 000 ... 000,100 ...000 and 111...111" is a binary representation of the data. We did not want to list all the 24 bits in there so it was listed as ‘…’ to signify that there are other bits at the middle.2. I can calculate Code = (2.56V x 1 x 2^16) / (1.024 x 2.56Vref) = 64000(H) = 0110 0100 0000 0000 0000. Is it correct?

Answer:The formula: Code = (AIN x GAIN x 2^n)/(1.024 x Vref) in which AIN depends on your analog input voltage, GAIN from 1~2.56V range and N = 24 because ADuC845 has 24 bit ADC. The 16 bit ADC that you’re referring is for ADuC848.3. I am wondering about the meaning of input voltage like zero differential, midscale and full scale. What is the reference for this definition in sight of input allowable voltage range

Answer:Zero differential means that you have equal voltage levels on the ADC’s negative and positive input, making the difference = 0. Midscale means that the ADC input is at the middle of the range, say Range = 0 to 2.5V, your mid scale input should be (2.5-0)/2 = 1.25V. While full scale means that the input voltage is equivalent to maximum range.4. With respect to GAIN, it is 1 at 2.56V range, and it is composed of 20mv units. Should the measured value be larger if Gain is large? If you look at the sample range, it looks like it's shrinking.

Answer:Yes, measured value will be larger at a larger Gain.5. On the same page, I want to know about the purpose and IEXC1 / 2.

Answer:IEXC1/2 is an Excitation current, it is configurable through Pins P1.6(AIN7) and P1.7(AIN8)(Refer to Rev. D Page 14 and Page 47 for more information).6. Could you explain the Sinc Filter 69 = decimal in figure 18.

Answer:Figure 18 shows the filter response when Chop is in with SF = 69. Sinc filter will help reduce the noise on ADC inputs by changing the ADC throughput rate (and cutoff frequencies)Regards,

AJ