I347-AT4 Datasheet, PDF (45/148 Pages) Intel Corporation – Intel® Ethernet Network Connection I347-AT4 Datasheet

Device Functionality—I347-AT4
Note that the maximum peak only measures up to about 200 meters of cable.
Vb
Va
Pb
Pa
Da
Db
Figure 14. First Peak Example
3.10.3
Offset
The offset reports the offset seen at the receiver. This is a debug mode. Bits 7:0 of
registers 16_5, 17_5, 18_5, and 19_5 have no meaning. When bits 15:8 return a value
of 0x80 it means there is zero offset. If bit 15:8 returns a value of 0x00 then the test
failed.
Note that in the maximum peak, first peak, and sample point modes, the systematic
offset is automatically subtracted from the results.
3.10.4
Sample Point
When register 20_8.7:6 is set to 11b, the amplitude of the reflected pulse at a
particular distance on the cable is reported. Unlike the maximum peak and first peak
modes which only measures up to about 200 meters of cable, the sample point mode
can measure up to 400 meters of cable.
The sample point returns the amplitude of the reflected pulse at a particular distance
on the cable. The distance is set by register 24_5.8:0. The threshold registers 25_5,
26_5, 27_5, 28_5.6:0, 25_7, 26_7, 27_7, and 28_7.6:0 are ignored.
Bits 7:0 of registers 16_5, 17_5, 18_5, and 19_5 return the same value as 24_5.7:0.
Note that register 24_5.8 is not returned. Bits 14:8 return the amplitude, and bit 15
the sign of the amplitude. If the test failed bits 15:8 returns 0x00000000 (zero
amplitude will always return as 0x10000000).
By programming register 24_5.8:0 from 0x000 to 0x1FF and running the sample point
test at each distance it is possible to reconstruct the reflected amplitude. Note that
since the threshold is ignored, it is possible that some small reflections in the same
channel measurements will be reported at short cable lengths when there are none.
This is because the analog hybrid does not 100% cancel out the transmitted signal.
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