ADAS1000-4BSTZ datasheet(54/80 Pages) AD

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ADAS1000-3/ADAS1000-4

Data Sheet

Rev. B | Page 54 of 80

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 was correctly received, software

should compute a CRC on both the data and the received

checksum. If data and checksum are received correctly, the

resulting CRC residue should equal 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 77. Input Clock

Clocks

The ADAS1000-3/ADAS1000-4 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 ADAS1000-3/ADAS1000-4 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 leads-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

ADAS1000-3/

ADAS1000-4

CLK_IO

ADAS1000-4BSTZ Datasheet(PDF) 54 Page - Analog Devices

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