SBAA106A June   2020  – August 2021 ADS112C04 , ADS112U04 , ADS114S06 , ADS114S08 , ADS122C04 , ADS122U04 , ADS1235 , ADS1235-Q1 , ADS124S06 , ADS124S08 , ADS1259 , ADS1259-Q1 , ADS125H01 , ADS125H02 , ADS1260 , ADS1260-Q1 , ADS1261 , ADS1262 , ADS1263 , ADS127L01 , ADS131A02 , ADS131A04 , ADS131M04 , ADS131M06 , ADS131M08

 

  1.   Trademarks
  2. 1Introduction
  3. 2Simple Checksum
    1. 2.1 Checksum Code Example
  4. 3CRC
    1. 3.1 CRC Generic Computations
      1. 3.1.1 Using XOR Bitwise Computation
      2. 3.1.2 Using Lookup Tables
        1. 3.1.2.1 Table Initialization
        2. 3.1.2.2 CRC Computation
      3. 3.1.3 CRC Computation Differences Between the ADS122U04 and ADS122C04
        1. 3.1.3.1 Byte Reflection Example
        2. 3.1.3.2 Reassembling Data Using Byte Reflection for CRC Computation
  5. 4Hamming Code
    1. 4.1 Hamming Code Computation
      1. 4.1.1 Hamming Code Computation Example
        1. 4.1.1.1 Counting Bits for Parity and Checksum Computations
          1. 4.1.1.1.1 Example of Counting Set Bits in the Data
          2. 4.1.1.1.2 Example of Counting Set Bits Using a Lookup Table
      2. 4.1.2 Validation of Transmitted Data
        1. 4.1.2.1 Hamming Validation
        2. 4.1.2.2 Checksum Validation
        3. 4.1.2.3 Error Correction
  6. 5Summary
  7. 6References
  8. 7Revision History

3.1.2 Using Lookup Tables

The lookup table requires a table of data for all of the possible combinations of remainders for any incoming byte of data. The table is stored in RAM or FLASH memory for quick access. The computation for the table entries use a method similar to the bitwise XOR when computing each table value. The number of table entries is 256 representing all combination of bits within a byte. Using a lookup table has the advantage of being on the order of four times faster than the bitwise operation and becomes comparable to the time it takes for a checksum operation at the expense of storing 512 bytes for 16-bit entries (256 bytes for 8-bit entries).