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Data Sheet

ADAS1000/ADAS1000-1/ADAS1000-2

CRC Word

Framed data integrity is provided by CRCs. For the 128 kHz

frame rates, the 16-bit CRC-CCITT polynomial is used. For the

2 kHz and 16 kHz frame rates, the 24-bit CRC polynomial used.

In both cases, the CRC residue is preset to all 1s and inverted

before being transmitted. The CRC parameters are summarized

in Table 24. To verify that data is correctly received, software

computes a CRC on both the data and the received checksum. If

data and checksum are received correctly, the resulting CRC

residue equals the check constant shown in Table 24. Note that

data is shifted through the generator polynomial MSB first, the

same order that it is shifted out serially. The bit and byte order

of the CRC that is appended to the frame is such that the MSB

of the CRC is shifted through the generator polynomial first in

the same order as the data so that the CRC residue XOR’d with

the inverted CRC at the end of the frame is all 1s, which is why

the check constant is identical for all messages. The CRC is

based only on the data that is sent out.

Figure 80. Input Clock

Clocks

The ADAS1000/ADAS1000-1/ADAS1000-2 run from an

external crystal or clock input frequency of 8.192 MHz.

The external clock input is provided for use in gang mode

so conversions between the two devices are synchronized.

In this mode, the CLK_IO pin is an output from the master

and an input from the slave. To reduce power, the CLK_IO is

disabled when not in gang mode. All features within the

ADAS1000 are a function of the frequency of the externally

applied clock. Using a frequency other than the 8.192 MHz

previously noted causes scaling of the data rates, filter corners,

ac lead off frequency, respiration frequency, and pace algorithm

corners accordingly.

Table 24. CRC Polynomials

Frame Rate

CRC Size

Polynomial

in Hex

Check Constant

2 kHz, 16 kHz

24 bits

x24 + x22 + x20 + x19 + x18 + x16 + x14 + x13 + x11 + x10 + x8 + x7 + x6 + x3 + x1 + x0

0x15D6DCB

0x15A0BA

128 kHz

16 bits

x16 + x12 + x5 + x0

0x11021

0x1D0F

XTAL1

XTAL2

ADAS1000

CLK_IO

Rev. B | Page 53 of 80

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