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Cortina Systems LXT9785 and LXT9785E Advanced 8-Port 10/100 Mbps PHY Transceivers
LXT9785/LXT9785E
Datasheet
249241, Revision 11.0
16 April 2007
4.11 DTE Discovery Process
If the link test function is disabled, the LXT9785/LXT9785E transmits to the connection
regardless of detected link pulses. The link test function is disabled by setting Register bit
16.14 = 1.
4.10.3.1
Link Failure
Link failure occurs if Link Test is enabled and link pulses or packets stop being received. If
this condition occurs, the LXT9785/LXT9785E returns to the auto-negotiation phase if
auto-negotiation is enabled.
4.10.4
Jabber
If a transmission exceeds the jabber timer, the LXT9785/LXT9785E disables the transmit
and loopback functions and the Collision Status bit (Register bit 17.11) is set regardless of
duplex. The jabber timer, according to the IEEE standard, must be between 20 ms to 150
ms. The RMII does not include a Jabber pin, but the MAC may read Register 1 to
determine jabber status. The LXT9785/LXT9785E automatically exits jabber mode after
the unjab time expires. This function is disabled by setting Register bit 16.10 = 1.
4.11
DTE Discovery Process
The DTE discovery process is port dependent and must be enabled through software.
The process is implemented as a next page option to the auto-negotiation flow. When the
process is enabled, manual control of auto-negotiation next pages is not allowed. This
feature applies to the LXT9785E transceiver only.
The process depends upon an IP phone, or any other DTE capable of being powered
remotely, having a specific filter that passes NLPs and FLPs. This filter should be non-
polarized to insure that the latest status of Auto-MDIX operation does not effect operation.
This filter attenuates 100 Mbps MLT3 signals and 10 Mbps Manchester-encoded signals,
and must be bypassed when power is applied to the IP phone.
Figure 29 shows a typical
IP telephone system connection.
Figure 29
Typical IP Telephone System Connection
Power
Outlet
Computer
12
3
45
6
78
9
*
8#
IP Telephone
UPS/
Generator
Power cable
SD
Powe r
Fa ult
12
34
5
6
7
8
9 1 01112
Li nk
Mode
Li nk
13 14 15 16 17 18
19
21
20
22 23 24
Mod e Se lect
Fd x
Act
1 X
2X
3X
4X
5X
6 X
7 X
8X
9X
10 X
11X
12X
13X
1 4X
1 5X
1 6X
17X
18X
19X
2 0X
2 1X
2 2X
23X
24X
1 0/100Base-T Ports
100
Reset
Clear
Mo du le Status
Se lf T est
Con sole
ProCurve Swi tch 2424M
HP J4122B
VoIP-Enabled Switch
Power
Outlet
Data only over
Category 5 cable
Power cable
Power and data over
Category 5 cable