Analog Devices ADuCM355 Hardware Reference Manual page 304

UG-1262
Polynomial
The CRC accelerator supports the calculation of the CRC using any length polynomial. The polynomial must be written to the
polynomial register. For MSB first implementation, omit the highest power while programming the CRC polynomial register and left
justify the polynomial. For LSB first implementation, right justify the polynomial and omit the LSB. The result register contains x-bit
MSBs as a checksum for an x-bit CRC polynomial.
The following examples illustrate the CRC polynomial.
16-Bit Polynomial Programming for MSB First Calculation
Polynomial: CRC-16-CCITT
16 12 5
x + x + x + 1 = (1) 0001 0000 0010 0001 = 0x1021
where the largest exponent (x
When left justified in the polynomial register, the register format is detailed in Table 397.
Table 397. 16-Bit Polynomial Programming Register Format, MSB First Calculation
Register
CRC Polynomial Register (POLY)
CRC Result Register (Result)
Initial Seed Programmed in CRC Result Register (Result)
16-Bit Polynomial Programming for LSB First Calculation
Polynomial: CRC-16-CCITT
16 12 5
x + x + x + 1 = 1000 0100 0000 1000 (1) = 0x8408
where the smallest exponent (x
When right justified in the polynomial register, the register format is detailed in Table 398.
Table 398. 16-Bit Polynomial Programming Register Format, LSB First Calculation
Register
CRC Polynomial Register (POLY)
CRC Result Register (Result)
Initial Seed Programmed in CRC Result Register (Result)
16
term) is implied. Therefore, the polynomial is 0001 0000 0010 0001.
0
term) is implied. Therefore, the polynomial is 1000 0100 0000 1000.
ADuCM355
Rev. B | Page 304 of 312
Hardware Reference Manual
Bit(s) Value
[31:24] 0001 0000
[23:16] 0010 0001
[15:8] 0x08B0
[7:0] 0x08B0
[31:24] CRC
[23:16] Result
[15:8] 0x08B0
[7:0] 0x08B0
[31:24] CRC
[23:16] Seed
[15:8] 0x08B0
[7:0] 0x08B0
Bit(s) Value
[31:24] 0x08B0
[23:16] 0x08B0
[15:8] 1000 0100
[7:0] 0000 1000
[31:24] 0x08B0
[23:16] 0x08B0
[15:8] CRC
[7:0] Result
[31:24] 0x08B0
[23:16] 0x08B0
[15:8] CRC
[7:0] Seed