DJLXT972ALC.A4 Cortina Systems Inc, DJLXT972ALC.A4 Datasheet - Page 26

• Manufacturer Part Number: DJLXT972ALC.A4
• Manufacturer: Cortina Systems Inc

Specifications of DJLXT972ALC.A4

• Lead Free Status / RoHS Status: Not Compliant

LXT972A PHY
Datasheet
249186, Revision 5.2
13 September 2007
Notes:
5.3.2
5.3.2.1
5.3.2.2
5.4
5.4.1
Cortina Systems
The digital and analog circuits require 3.3 V supplies (VCCA and VCCD). These inputs
may be supplied from a single source. Each supply input must be de-coupled to ground.
An additional supply may be used for the MII (VCCIO). The supply may be either 2.5 V or
3.3 V. Also, the inputs on the MII interface are tolerant to 5 V signals from the controller on
the other side of the MII interface. For MII I/O characteristics, see
Characteristics
Clock Requirements
External Crystal/Oscillator
The LXT972A PHY requires a reference clock input that is used to generate transmit
signals and recover receive signals. It may be provided by either of two methods: by
connecting a crystal across the oscillator pins (XI and XO) with load capacitors, or by
connecting an external clock source to pin XI.
The connection of a clock source to the XI pin requires the XO pin to be left open. To
minimize transmit jitter, Cortina recommends a crystal-based clock instead of a derived
clock (that is, a PLL-based clock).
A crystal is typically used in NIC applications. An external 25 MHz clock source, rather
than a crystal, is frequently used in switch applications. For clock timing requirements, see
Table 24, I/O Characteristics - REFCLK/XI and XO Pins, on page
MDIO Clock
The MII management channel (MDIO) also requires an external clock. The managed data
clock (MDC) speed is a maximum of 8 MHz.
Initialization
This section includes the following topics:
When the LXT972A PHY is first powered on, reset, or encounters a link failure state, it
checks the MDIO register configuration bits to determine the line speed and operating
conditions to use for the network link.
Table 13
set by the Hardware Control or MDIO interface.
MDIO Control Mode and Hardware Control Mode
In the MDIO Control mode, the LXT972A PHY reads the Hardware Control Interface pins
to set the initial (default) values of the MDIO registers. Once the initial values are set, bit
control reverts to the MDIO interface.
The following modes are available using either Hardware Control or MDIO control:
®
1. Bring up power supplies as close to the same time as possible.
2. As a matter of good practice, keep power supplies as clean as possible.
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LXT972A Single-Port 10/100 Mbps PHY Transceiver
Section 5.4.1, MDIO Control Mode and Hardware Control Mode
Section 5.4.2, Reduced-Power Modes
Section 5.4.3, Reset
Section 5.4.4, Hardware Configuration Settings
shows the LXT972A PHY initialization sequence. The configuration bits may be
1
- MII Pins, on page
52.
53.
Table 23, Digital I/O
5.4 Initialization
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