TIC10024-Q1 Datasheet, PDF (25/81 Pages) Texas Instruments – 24-Input Multiple Switch Detection Interface (MSDI) Device With Adjustable Wetting Current for Automotive Systems

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TIC10024-Q1
SCPS268 – SEPTEMBER 2017
8.3.12 Cyclic Redundancy Check (CRC)
The TIC10024-Q1 includes a CRC module to support redundancy checks on the configuration registers to
ensure the integrity of data. The CRC calculation is based on the ITU-T X.25 implementation, and the CRC
polynomial (0x1021) used is popularly known as CRC-CCITT-16 since it was initially proposed by the ITU-T
(formerly CCITT) committee. The CRC calculation rule is defined in Table 3:
CRC RULE
CRC result width
Polynomial
Initial (seed) value
Input data reflected
Result data reflected
XOR value
Table 3. CRC Calculation Rule
VALUE
16 bits
x¹⁶ + x¹² + x⁵ +1 (1021h)
FFFFh
No
No
0000h
The CRC calculation is done on all the configuration registers starting from register CONFIG and ending at the
last reserved register at address 32h. The device substitutes a “zero” for each reserved configuration register bit
during the CRC calculation. The CRC calculation can be triggered by asserting the CRC_T bit in the CONFIG
register. Once completed, the CRC_CALC interrupt bit in the INT_STAT register is asserted and an interrupt is
issued. The 16-bit CRC calculation result is stored in the register CRC. This interrupt can be disabled by de-
asserting the CRC_CALC_EN bit in the INT_EN_CFG0 register. It is important to avoid writing data to the
configuration registers when the device is undergoing CRC calculations to prevent false calculation results.
Figure 16 shows the block diagram of the CRC module. The module consists of 16 shift-registers and 3
exclusive-OR gates. The registers start with 1111-1111-1111-1111 (or FFFFh) and the module performs an XOR
function and shifts its content until the last bit of the register string is used. The final register’s content after the
last data bit is the calculated CRC value of the data set and the content is stored in the CRC register.
Note the CRC_T bit self-clears after the CRC calculation is completed. Logic 1 is used for CRC_T bit during CRC
calculation.
X15 X14 X13 X12
X11 X10 X9 X8 X7 X6 X5
X4 X3 X2 X1 X0
XOR ⁺
+
XOR
+
XOR
Data
MSB
LSB
Figure 16. CCITT-16 CRC Module Block Diagram
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