Datasheet

AD7760
Rev. A | Page 32 of 36
Table 13 shows the hexadecimal values (in sign-and-magnitude
format) that are downloaded to the AD7760 to realize this filter.
The table is also split into the bytes that are summed to produce
the checksum. The checksum generated from these coefficients
is 0x0E6B.
Table 13. Filter Hexadecimal Values
Word 1 Word 2
Coefficient Byte 1 Byte 2 Byte 3 Byte 4
1 03 2B 96 88
2 01 BF 18 3C
3 00 15 66 26
4 04 A8 1E 6A
5 04 5F 2A 96
6 00 2C 49 C2
7 00 50 E9 F6
8 00 10 DB D8
9 04 2F DE 54
10 04 37 44 5A
11 04 1B 7D 6E
12 04 04 3B 5F
Table 14 lists the 16-bit words the user would write to the
AD7760 to set up the ADC and download this filter, assuming
an output data rate of 1.25 MHz has been selected.
Table 14. Sequence of Write Instructions to Set Up Device
and Download the Filter Example
Word Description
0x0001 Address of Control Register 1.
0x8079
Control register data. DL filter: set filter length = 24,
set output data rate = 1.25 MHz.
0x032B First coefficient, Word 1.
0x9688 First coefficient, Word 2.
0x01BF Second coefficient, Word 1.
0x183C Second coefficient, Word 2.
…
Other coefficients.
0x0404 Twelfth (final) coefficient, Word 1.
0x3B5F Final coefficient, Word 2.
0x0E6B
Checksum. Wait (0.5 × t
ICLK
× number of unused
coefficients) for AD7760 to write 0s to the remaining
unused coefficients.
0x0001 Address of control register.
0x0879
Control register data. Set read status and maintain
filter length and decimation settings. Read contents
of status register. Check Bit 7 (DL_OK) to determine
if the filter was downloaded correctly.