Datasheet

DP83640
SNOSAY8E –SEPTEMBER 2007–REVISED APRIL 2013 www.ti.com
10.4.3 TDR Control Register (TDR_CTRL), Page 2
This register contains control for the Time Domain Reflectometry (TDR) cable diagnostics. The TDR cable
diagnostics sends pulses down the cable and captures reflection data to be used to estimate cable length
and detect certain cabling faults.
Table 10-30. TDR Control Register (TDR_CTRL), address 0x16
Bit Bit Name Default Description
15 TDR_ENABLE 0, RW TDR Enable:
Enable TDR mode. This forces the powerup state to the correct operating
condition for sending and receiving TDR pulses.
14 TDR_100Mb 0, RW TDR 100Mb:
Sets the TDR controller to use the 100 Mb Transmitter. This allows for
sending pulse widths in multiples of 8ns. Pulses in 100 Mb mode will
alternate between positive pulses and negative pulses.
Default operation uses the 10 Mb Link Pulse generator. Pulses may
include just the 50 ns pre-emphasis portion of the pulse or the 100 ns full
link pulse (as controlled by setting TDR Width).
13 TX_CHANNEL 0, RW Transmit Channel Select:
Select transmit channel for sending pulses. The pulse can be sent on the
Transmit or Receive pair.
0 : Transmit channel
1 : Receive channel
12 RX_CHANNEL 0, RW Receive Channel Select:
Select receive channel for detecting pulses. The pulse can be monitored
on the Transmit or Receive pair.
0 : Transmit channel
1 : Receive channel
11 SEND_TDR 0, RW/SC Send TDR Pulse:
Setting this bit will send a TDR pulse and enable the monitor circuit to
capture the response. This bit will automatically clear when the capture is
complete.
10:8 TDR_WIDTH 000, RW TDR Pulse Width:
Pulse width in clocks for the transmitted pulse. In 100 Mb mode, pulses
are in 8 ns increments. In 10 Mb mode, pulses are in 50 ns increments,
but only 50 ns or 100 ns pulses can be sent. Sending a pulse of 0 width
will not transmit a pulse, but allows for baseline testing.
7 TDR_MIN_MODE 0, RW Min/Max Mode control:
This bit controls direction of the pulse to be detected. Default looks for a
positive peak. Threshold and peak values will be interpreted appropriately
based on this bit.
0 : Max Mode, detect positive peak
1 : Min Mode, detect negative peak
6 RESERVED 0, RW RESERVED: Must be zero.
5:0 RX_THRESHOLD 10 0000, RW RX Threshold:
This value provides a threshold for measurement to the start of a peak. If
Min Mode is set to 0, data must be greater than this value to trigger a
capture. If Min Mode is 1, data must be less than this value to trigger a
capture. Data ranges from 0x00 to 0x3F, with 0x20 as the midpoint.
Positive data is greater than 0x20, negative data is less than 0x20.
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