Datasheet

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DP83849C
7.3.3 TDR Control Register (TDR_CTRL), Page 2, address 16h
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 45. TDR Control Register (TDR_CTRL), address 16h
Bit Bit Name Default Description
15 TDR_ENABLE 0, RW TDR Enable:
Enable TDR mode. This forces powerup state to correct operating
condition for sending and receiving TDR pulses.
14 TDR_100Mb 0, RW TDR 100Mb:
Sets TDR controller to use the 100Mb Transmitter. This allows for
sending pulse widths in multiples of 8ns. Pulses in 100Mb mode
will alternate between positive pulses and negative pulses.
Default operation uses the 10Mb Link Pulse generator. Pulses may
include just the 50ns preemphasis portion of the pulse or the 100ns
full link pulse (as controlled by setting TDR Width).
13 TX_CHANNEL 0, RW Transmit Channel Select:
Select transmit channel for sending pulses. 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. Pulse can be moni-
tored 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 0, RW TDR Pulse Width:
Pulse width in clocks for the transmitted pulse. In 100Mb mode,
pulses are in 8ns increments. In 10Mb mode, pulses are in 50ns
increments, but only 50ns or 100ns 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, RO RESERVED: Writes ignored, read as 0.
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.