KSZ9031RNX(2012) Ver la hoja de datos (PDF) - Micrel

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componentes Descripción

Fabricante

KSZ9031RNX
(Rev.:2012)

Gigabit Ethernet Transceiver with RGMII Support

Micrel 

Micrel, Inc.

KSZ9031RNX

Pad Skew (value)

0000

0001

0010

0011

0100

0101

0110

0111

1000

1001

1010

1011

1100

1101

1110

1111

Delay (ns)

–0.42

–0.36

–0.30

–0.24

–0.18

–0.12

–0.06

No delay adjustment (default value)

+0.06

+0.12

+0.18

+0.24

+0.30

+0.36

+0.42

+0.48

Table 6. Absolute Delay for 4-bit Pad Skew Setting

When computing the RGMII timing relationships, delays along the entire data path must be aggregated to determine the

total delay to be used for comparison between RGMII pins within their respective timing group. For the transmit data path,

total delay includes MAC output delay, MAC-to-PHY PCB routing delay, and PHY (KSZ9031RNX) input delay and skew

setting (if any). For the receive data path, the total delay includes PHY (KSZ9031RNX) output delay, PHY-to-MAC PCB

routing delay, and MAC input delay and skew setting (if any).

After power-up or reset, the KSZ9031RNX defaults to the following timings at its RGMII I/O pins to support on-chip data-

to-clock skew timing according to the RGMII Version 2.0 Specification:

• Transmit Inputs:

GTX_CLK clock is in sync within ±500ps of TX_EN and TXD[3:0]

• Receive outputs:

RX_CLK is delayed about 1.2ns with respect to RX_DV and RXD[3:0]

The above default RGMII timings imply:

• RX_CLK clock skew is set by the KSZ9031RNX default register settings.

• GTX_CLK clock skew is provided by the MAC.

• No PCB delay is required for GTX_CLK and RX_CLK clocks.

The following examples show how to read/write to MMD Address 2h, Register 8h for the RGMII GTX_CLK and RX_CLK

skew settings. MMD register access is through the direct portal registers Dh and Eh. For more programming details, refer

to the “MMD Registers – Descriptions” section.

• Read back value of MMD Address 2h, Register 8h.

- Write register 0xD = 0x0002 // Select MMD Device Address 2h

- Write register 0xE = 0x0008 // Select register 8h of MMD Device Address 2h

- Write register 0xD = 0x4002 // Select register data for MMD Device Address 2h, register 8h

- Read register 0xE

// Read value of MMD Device Address 2h, Register 8h

October 2012

26

M9999-103112-1.0

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